THE  LIGHTING  ART 


BOOKS  BY  THE  SAME  AUTHOR 


COLOR  AND  ITS  APPLICATIONS  (1915). 
360  Pages,  129  Illustrations,  21  Tables,  and  4  Color 
Plates. 

LIGHT  AND  SHADE  AND  THEIR  APPLICATIONS  (1916). 
277  Pages,  135  Illustrations,  10  Tables, 
D.  Van  Nostrand  Co.,  New  York. 

THE  LIGHTING  ART  (1917). 
224  Pages,  43  Illustrations,  9  Tables, 
McGraw-Hill  Book  Company,  Inc.,  New  York. 

THE  LANGUAGE  OP  COLOR.  In  Press. 

Dodd  Mead  and  Co.,  New  York. 


THE  LIGHTING  ART 


ITS  PRACTICE 
AND  POSSIBILITIES 


BY 

M.  I^UCKIESH 


PHYSICIST,    NELA   RESEARCH   LABORATORY 
NATIONAL  LAMP   WORKS   OF  GENERAL  ELECTRIC  COMPANY. 


FIRST  EDITION 


McGRAW-HILL  BOOK  COMPANY,  INC. 
239  WEST  39TH  STREET.    NEW  YORK 


LONDON:  HILL  PUBLISHING  CO.,  LTD. 

6  &  8  BOUVERIE  ST..  E.  C. 

1917 


COPYRIGHT,  1917,  BY  THE 
MCGRAW-HILL  BOOK  COMPANY,  INC. 


THE  MAPLE  PRESS  YORK  PA 


~Dc6lcate6  to 

THE  RELATIVELY  SMALL  GROUP  OP  MEN  WHOSE  UNSELFISH  EFFORTS  IN 

LIGHTING  ARE  DIRECTED  TOWARD  THE  CONSERVATION  OF  VISION 

— THAT  MOST  VALUABLE  HUMAN  RESOURCE — AND  TOWARD 

THE   INCREASE    IN    THE    SAFETY,   THE   EFFICIENCY, 

AND    THE    PLEASURE    OF   MANKIND    THROUGH 

THE   APPLICATIONS     OF     LIGHT — THAT 

MOST  POTENT  NATURAL  AGENCY. 


384421 


PREFACE 

Mankind  has  enjoyed  such  an  abundance  of  natural  day- 
light throughout  the  entire  existence  and  evolution  of  the 
human  race  that  the  present  general  indifference  to  the  possi- 
bilities in  lighting  is  easily  accounted  for.  With  the  advent  of 
artificial  light-sources  of  greater  adaptability,  the  activities  of 
man  changed  considerably  and  as  modern  artificial  illuminants 
are  readily  controllable  there  naturally  has  arisen  a  new  science 
and  art,  namely,  that  of  lighting.  Such  desirable  features  as 
adaptability  and  controllability  often  result  in  misuses  of  arti- 
ficial light  at  the  hands  of  those  who  are  indifferent  to  or  un- 
trained in  the  proper  use  of  light.  This  together  with  the 
greatly  increased  possibilities  led  to  the  development  of  special- 
ists in  lighting  and,  owing  to  his  connection  with  many  of  the 
activities  upon  which  the  production  of  light  depends,  the 
engineer  became  the  embryo  from  which  the  so-called  illumi- 
nating engineer  of  today  evolved. 

As  the  efficiency  and  adaptability  of  artificial  light-sources 
and  the  knowledge  of  the  importance  of  proper  lighting  devel- 
oped, the  demands  upon  the  engineer  became  more  varied 
until  today  when  the  many  aspects  and  possibilities  are  becom- 
ing more  appreciated,  the  engineer  must  greatly  extend  his 
horizon  and  knowledge  in  order  to  qualify  as  a  lighting  specialist 
in  the  broadest  sense.  Notwithstanding  the  extensive  possibili- 
ties in  lighting  at  the  present  time  and  the  myriad  ramifications 
of  the  attendant  problems  into  various  sciences  and  arts,  there 
is  still  a  tendency  on  the  part  of  many  to  look  upon  a  lighting 
problem  primarily  from  the  engineering  standpoint  regardless 
of  the  nature  of  the  problem. 

Bearing  witness  to  this  fact  are  the  books  on  lighting  which 
consist  largely  of  engineering  data  and  considerations.  A  vast 
amount  of  lighting  which  has  been  well  done,  has  been  accom- 
plished through  applications  of  scientific  and  artistic  principles 
not  covered  by  engineering  data.  However,  the  latter  are  of 


viii  PREFACE 

great  value  and  there  is  no  intention  on  my  part  to  depreciate 
their  value.  These  data  have  a  definite  place  in  lighting  and 
they  have  aided  to  no  small  degree  in  the  development  of  light- 
ing practice.  But  in  practising  lighting  from  the  engineer's 
viewpoint  dominantly  and  persistently,  the  results  are  natu- 
rally those  of  illuminating  engineering.  However  if  lighting  be 
practised  from  that  broader  viewpoint  of  the  lighting  specialist 
who  has  become  familiar  with  the  sciences  and  arts  into  which 
the  problems  lead,  the  results  will  be  more  worthy  of  the  poten- 
tiality of  light. 

The  purpose  of  this  book  is  to  discuss  lighting  broadly  from 
an  unusual  viewpoint.  Engineering  and  scientific  data  may 
be  found  elsewhere  in  great  abundance  so  that  the  following 
chapters  will  be  confined  to  discussions  of  many  scientific  and 
artistic  aspects  of  lighting  with  the  aim  to  indicate  greater 
possibilities  in  the  use  of  light.  Believing  that  discussions  of 
principles  aid  in  cultivating  creative  ability  I  have  given  un- 
usual prominence  to  this  aspect  of  lighting. 

It  is  a  pleasant  duty  to  acknowledge  my  gratitude  to  the 
management  of  the  National  Lamp  Works  of  the  General 
Electric  Company  for  the  facilities  which  I  have  enjoyed  in 
the  study  of  lighting  and  to  Dr.  E.  P.  Hyde,  Director  of  Nela 
Research  Laboratory,  for  placing  these  facilities  at  my  disposal. 

M.  LUCKIESH. 

October,  1917. 


CONTENTS 


CHAPTER  PAGE 

PREFACE vii 

I.    THE  BROAD  ASPECT  OF  LIGHTING i 

II.    EXPRESSIVE  POSSIBILITIES  OF  LIGHT 10 

III.  VISUALIZATION    . 16 

IV.  VARIETY — THE  SPICE  OF  LIGHTING 21 

V.     DISTRIBUTION  OF  EIGHT 27 

VI.    LIGHTING  FIXTURES 38 

VII.    LIGHT  AND  COLOR 48 

VIII.    COLORED  ILLUMINANTS 60 

IX.    THE  PSYCHO-PHYSIOLOGY  OF  COLOR 71 

X.    SIMULATING  THE  SPECTRUM  OF  DAYLIGHT 80 

XI.    APPLICATIONS  OF  ARTIFICIAL  DAYLIGHT 85 

XII.     SOME  APPLICATIONS  OF  COLORED  LIGHT 94 

XIII.  SIMPLE  PRINCIPLES  OF  LIGHT-CONTROL ici 

XIV.  LIGHTING  AND  ARCHITECTURE 113 

XV.    THE  PORTABLE  LIGHTING  UNIT 122 

XVI.    RESIDENCE  LIGHTING 132 

XVII.    COMMERCIAL  LIGHTING 147 

XVIII.    LIGHTING  IN  PUBLIC  BUILDINGS 158 

XIX.    INDUSTRIAL  LIGHTING 171 

XX.     STAGE-LIGHTING 180 

XXI.     SPECTACULAR  LIGHTING 189 

XXII.     COMPUTATIONS  AND  DATA 197 

XXIII.  NATURAL  LIGHTING 210 

XXIV.  THE  LANGUAGE  OF  COLOR 217 

INDEX    .   .                                                                           225 


IX 


THE  LIGHTING  ART 

ITS   PRACTICE  AND  POSSIBILITIES 

CHAPTER  I 
THE  BROAD  ASPECT  OF  LIGHTING 

Light  is  one  of  the  dominating  agencies  in  life  and  progress, 
for  it  is  essential  to  our  most  important  and  educative  sense — 
vision.  The  possibilities  of  lighting  extend  into  all  those  activi- 
ties which  make  their  appeal  to  human  consciousness  through 
the  doorway  of  vision.  The  importance  of  lighting  is  limited 
only  by  the  boundaries  of  human  activities  and  in  the  broadest 
sense  its  importance  extends  even  beyond  them,  for  it  is  one 
of  the  most  prominent  factors  in  the  scheme  of  creation.  The 
activities  of  primitive  man  were  practically  bounded  by  sun- 
rise and  sunset,  and  darkness  was  feared  and  avoided  as  the 
abode  of  evil  spirits  and  of  lurking  dangers.  We  may  imagine 
a  growing  desire  for  independence  which  resulted  in  the  making 
of  fire  by  those  primitive  beings.  Doubtless  light  was  merely 
a  by-product  of  the  fire  whose  primary  function  was  to  furnish 
heat;  nevertheless  we  may  imagine  primitive  man  with  his 
burning  pine  knot  exultant  in  his  victory  over  Nature.  This 
achievement  was  one  of  the  first  important  milestones  on  the 
highway  of  human  progress.  Man's  activities  were  no  longer 
limited  to  daylight  hours  and  greater  opportunities  were  before 
him. 

We  inherit  the  primitive  instincts  of  the  impressiveness  of 
light,  color  and  darkness  and  this  heritage  combined  with  the 
cultivation  of  the  esthetic  sense  provides  a  vast  field  of  appeal 
for  lighting  effects  properly  tuned  to  awaken  the  responsive 
chords.  In  a  broad  sense  lighting  has  potential  possibilities 
in  connection  with  all  the  arts,  such  as  decoration,  painting, 
sculpture,  and  architecture  which  employ  light,  shade,  and 

1 


2  THE  LIGHTING  ART 

color.  .  But  lighting  possesses  a  potentiality  exceeding  the 
media  employed  in  such  arts  for  it  deals  with  " primary"  light 
whose  expressive  and  imitative  possibilities  are  limited  only 
by  the  capacity  of  the  sense  of  vision.  The  media  employed 
in  the  arts  strive  to  imitate  light  but  their  ranges  are  bounded 
by  the  extreme  limitations  of  transmitting  and  reflecting 
media.  This  aspect  of  lighting  is  perhaps  the  least  developed 
of  any  of  the  many  phases  of  possibilities  because  lighting- 
artists  have  barely  entered  the  field,  Nevertheless,  it  appears 
that  in  expressiveness  and  impressiveness  in  lighting  lies  one 
of  the  greatest  fields  for  future  development. 

Returning  to  the  purely  utilitarian  aspect  of  lighting  we 
find  unnumbered  centuries  elapsed  between  the  first  burning 
fagot  and  the  advent  of  the  grease  lamp  and  the  wax  candle. 
Then  the  tallow  candle  appeared  and  its  use  extends  to  the 
present  time — a  connecting  link  to  the  per  od  when  practicable 
artificial  light-sources  were  first  available.  From  this  retro- 
spective view  springs  the  realization  that  artificial  lighting 
worthy  of  the  name  is  a  development  of  a  comparatively  modern 
period.  In  reality  it  is  difficult  to  note  the  place  where  science 
entered  the  field  of  light-production.  In  a  sense  it  has  always 
been  present  for  that  which  changes  the  mysteries  of  today 
into  commonplace  facts  of  tomorrow  is  science,  in  whatever 
guise. 

However,  as  we  look  backward,  science  as  we  define  it  today 
really  attacked  the  problem  of  light-production  in  an  organized 
manner  not  many  years  ago.  The  results  which  followed  in 
rapid  succession  yielded  the  oil  lamp,  gas  jets  and  mantles. 
Reinforced  by  electrical  development,  science  gave  to  the  world 
the  arcs  and  incandescent  lamps.  With  an  ever-increasing 
momentum  these  lamps  were  improved,  new  materials  were 
discovered,  and  better  manufacturing  processes  were  developed 
with  the  result  that  in  the  last  25  years  remarkable  progress 
has  been  made  in  light  production. 

When  it  is  noted  that  the  lemarkable  industrial  progress  of 
the  past  century  is  coincident  with  the  great  progress  in  light- 
production  one  cannot  avoid  the  conclusion  that  this  is  not 
merely  a  coincidence.  Perhaps  a  future  superhuman  stat- 


THE  BROAD  ASPECT  OF  LIGHTING  3 

istician  will  be  able  to  look  back  upon  these  two  parallel  lines 
of  progress  and  credit  lighting  with  no  small  responsibility  in 
the  momentous  industrial  development  of  the  present  age. 
Man  now  pursues  his  activities  wherever  he  desires  quite  inde- 
pendent of  daylight.  Industries  continue  24  hours  per  day 
which  at  least  doubles  the  production  of  an  equipment  pre- 
viously dependent  upon  natural  lighting.  In  crowded  smoky 
cities  artificial  light  is  often  depended  upon  entirely.  New  arts 
have  developed  with  the  advent  of  effective  artificial  lighting 
and  our  living  conditions  have  been  so  altered  that  artificial 
lighting  is  a  very  essential  factor.  Incidentally,  a  vast  number 
of  persons  find  little  time  to  recreate  and  to  cultivate  the 
intellect  except  with  the  aid  of  artificial  lighting,  which  suggests 
economic  and  even  sociological  aspects  worthy  of  consideration. 
Owing  to  changed  conditions  of  working  even  natural  daylight 
may  no  longer  be  considered  to  be  tree  from  cost  when  admitted 
into  those  interiors  where  industrial  and  commercial  activities 
,  are  pursued.  From  an  architectural  standpoint  natural  day- 
lighting  must  bear  a  certain  investment  and  maintenance  cost. 
In  our  crowded  cities  natural  lighting  must  be  charged  with  no 
inappreciable  amount  for  the  floor  and  wall  area  sacrificed,  and 
in  various  minor  ways  the  cost  of  natural  daylight  indoors 
increases.  Although  no  figures  are  available  it  appears  reason- 
able to  conclude,  on  bringing  into  consideration  the  element 
of  satisfactoriness  that  there  are  many  places  where  artificial 
lighting  may  compete  with  natural  lighting  on  the  basis  of  cost. 
This  is  an  aspect  woithy  of  future  consideration.  At  present 
the  psychological  effect  of  excluding  daylight  would  develop 
opposition  to  such  a  proposal  but  night-workers  and  many 
day-workers  are  content  without  it  if  the  artificial  lighting  is 
reasonably  satisfactory.  With  the  ever-increasing  congestion, 
the  cost  of  floor  and  wall  space,  and  the  necessity  for  the  most 
efficient  operation  of  industrial  and  commercial  plants,  the  cost 
of  daylight  will  be  given  more  attention.  Aspects  such  as 
ventilation  and  the  hygienic  influence  of  sunlight  will  doubtless 
be  met  by  science  and  it  is  not  unreasonable  to  suggest  a  greater 
independence  from  daylight  in  the  future. 

But  with  the  increasing  demands  upon  artificial  lighting  and 


4  THE  LIGHTING  ART 

with  the  development  of  light-sources  of  higher  efficiency,  which 
has  been  attended  usually  by  more  powerful  light-sources  of 
higher  intrinsic  brightnesses,  dangers  of  misuses  of  light  arose. 
As  we  look  back  at  any  of  the  early  practicable  artificial 
illuminants  of  the  past  century  we  might  sincerely  feel, 

"  'Twas  a  light  that  made 
Darkness  itself  appear 
A  thing  of  comfort," 

owing  to  the  feeble  efforts  which  those  illuminants  were  capable 
of  exerting  against  the  ever-crowding  darkness.  Today  the 
same  sentiment  is  appropriate  but  for  an  opposite  reason.  As 
we  look  about  us  at  the  powerful  exposed  light-sources  of  high 
intrinsic  brightness,  the  severe  contrasts  of  brightness,  the  bad 
positions  of  the  lighting  units,  the  harsh  shadows,  and  the 
absence  of  artistic  results  we  may  readily  subscribe  to  the 
same  sentiment.  In  the  first  case  those  words  were  quoted 
through  pity  but  in  the  last  case  through  anguish,  physical  and 
mental.  Thus  in  our  imagination,  as  we  traverse  only  a  part 
of  a  century,  we  find  ourselves  in  this  brief  period  first  extend- 
ing sympathy  to  the  feeble  light-sources  in  their  battle  against 
darkness  which  threatened  to  overwhelm  them  and  shortly 
the  tables  are  turned  and  we  find  ourselves  begging  for  relief 
against  powerful  glaring  light-sources. 

The  foregoing  picture  is  correct  in  its  general  features  but 
unfortunately  it  is  unnoticed  by  a  vast  majority  of  persons 
whose  eyesight,  disposition,  efficiency  and  safety  are  con- 
stantly being  jeopardized.  Throughout  his  entire  evolution, 
man  has  been  supplied  with  an  abundance  of  natural  day- 
light and,  after  momentarily  exulting  when  he  discovered  a 
process  of  making  fire  and  simultaneously  of  producing  artificial 
light,  he  again  relapsed  into  that  placid  indifference  toward 
lighting  which  persists  among  a  vast  majority  of  persons  even 
today.  This  indifference  is  one  of  the  chief  obstacles  in  the 
way  of  lighting  progress.  A  comparatively  small  number  of 
persons,  whose  activities  brought  them  especially  in  touch  with 
the  harmful  effects  of  bad  lighting  and  with  the  great  possi- 
bilities of  proper  lighting,  has  set  about  to  protect  the  eyesight 


THE  BROAD  ASPECT  OF  LIGHTING  5 

of  the  race  and  to  increase  the  safety,  the  efficiency,  and  the 
happiness  of  mankind  through  the  agency  of  lighting.  This 
was  the  definite  beginning  of  a  new  art  and  science  and,  owing 
to  his  intimate  contact  with  various  activities  closely  related 
to  lighting  such  as  gas  and  electrical  engineering,  the  engineer 
assumed  the  responsibilities  of  lighting;  hence  the  advent  of 
the  illuminating  engineer. 

In  the  early  days  of  lighting  as  a  distinct  profession,  the 
engineering  aspects  were  given  prominence.  In  fact,  lighting 
is  practised  today  largely  from  this  standpoint  notwithstand- 
ing that  the  efficiency  and  adaptability  of  modern  illuminants 
have  made  possible  the  realization  of  the  extension  of  lighting 
to  meet  very  largely  all  the  requirements  of  human  activities 
and  desires  in  respect  to  this  agency.  With  this  growing  atten- 
tion to  lighting  we  find  as  in  many  other  activities,  that  the 
deeper  we  delve  the  more  extensive  are  the  ramifications  and 
comparatively  smaller  is  the  part  of  the  apparent  whole  with 
which  we  are  thoroughly  familiar.  For  this  reason,  the 
physiologist  and  ophthalmologist  have  been  attracted  to  the 
problems  of  lighting  which  involve  the  visual  organs;  the 
physicist  specializes  in  many  of  the  problems  of  production 
and  utilization  of  light;  the  psychologist  finds  an  unexplored 
field  for  his  endeavors  for  finally  the  product  of  lighting  is 
largely  psychological;  the  artist  finds  an  outlet  for  his  ability 
in  clothing  scientific  lighting  principles  with  artistic  exteriors 
in  lighting  fixtures,  also  in  using  lighting  as  a  decorative 
medium  by  " painting"  with  light  as  obtained  primarily  from 
the  lighting  units.  As  we  delve  deeper  into  the  problem  of 
lighting  we  find  many  intimate  relations  between  lighting  and 
the  various  sciences  and  arts  all  of  which  must  be  appreciated 
by  the  lighting  practitioner  before  he  is  worthy  of  the  title  of 
lighting  expert. 

The  illuminating  engineer  should  recognize  that  the  esthetic 
sense,  however  dormant,  is  possessed  by  all  human  beings  as 
is  evidenced  by  the  things  about  us.  Perhaps  we  would  not 
apply  the  term,  artistic,  to  many  of  the  scenes  which  greet  us 
during  our  daily  routine;  however,  as  we  critically  view  any  of 
these  scenes  and  eliminate  in  our  imagination  all  that  is  not 


6  THE  LIGHTING  ART 

purely  utilitarian,  how  different  they  would  appear!  Imagine 
this  done  to  everything  on  earth  and  a  fair  appreciation  of  the 
value  of  the  artistic  and  beautiful  is  obtained.  On  the  other 
hand,  the  artist  should  appreciate  that  in  a  broad  sense  in 
lighting,  utility  cannot  be  divorced  from  beauty.  In  fact,  it  is 
misleading  to  use  these  two  terms  as  if  they  had  nothing  in 
common.  Beauty  in  itself  is  certainly  useful  as  viewed  from 
the  broad  outlook  upon  life.  Conversely,  if  a  lighting  fixture 
is  intended  to  supply  illumination  for  a  utilitarian  purpose 
and  it  fails  to  perform  this  function  properly,  it  cannot  be  con- 
sidered strictly  beautiful  regardless  of  its  grace  of  line  and  of 
its  proportions.  The  philosophy  of  the  beautiful  teaches  us  that 
beauty  is  the  result  of  a  harmonious  ensemble  of  the  various 
parts,  hence  in  lighting  fixtures  beauty  in  a  broad  sense  is 
dependent  upon  the  harmony  of  science  and  art.  In  the  design 
of  fixtures  we  have  a  definite  ground  on  which  science  and  art 
should  harmoniously  intermingle. 

But  the  consideration  of  the  artistic  aspect  of  lighting  should 
not  end  at  the  fixtures.  In  fact,  the  greater  field  lies  beyond 
them  in  the  distribution  of  light  upon  the  various  surfaces  such 
as  ceiling,  walls  and  floor,  in  the  production  of  shadows  appro- 
priate to  the  setting  and  in  the  color  which  best  fits  the  spirit 
or  mood  of  the  room  or  of  the  occasion.  This  is  the  most 
neglected  aspect  of  lighting  although  it  is  one  of  the  most 
extensive  fields  for  development.  Inasmuch  as  the  prime  object 
of  the  lighting  specialist  is  to  safeguard  vision  he  seeks  for 
rules  which  limit  brightnesses  and  brightness-contrasts  to 
safe  values.  Research  is  contributing  much  of  value  by  direct 
attack  on  these  problems.  However,  a  rule  which  appears  a 
safe  one  to  follow,  in  the  absence  of  any  other  simple  and  specific 
rule,  is  that  if  the  lighting  does  not  offend  the  finer  esthetic 
sensibilities  it  is  not  likely  to  be  seriously  harmful  in  its  physio- 
logical effects.  Such  a  rule  cannot  be  applied  safely  as  a 
criterion  of  the  best  possible  illumination  but  glaring  lighting 
conditions  have  no  place  in  an  esthetic  harmony  of  light,  shade 
and  color. 

A  specific  aspect  of  lighting  included  in  the  preceding  general 
discussion  is  the  relation  of  lighting  to  architecture.  The 


THE  BROAD  ASPECT  OF  LIGHTING  7 

appeal  of  architecture  is  chiefly  through  vision  and  the  impres- 
sion of  proper  proportions,  of  decorative  value  of  details,  and 
the  harmony  of  the  whole  is  gained  through  the  distribution  of 
light,  shade,  and  color.  Form  and  color  are  chief  elements 
but  lighting  is  of  extreme  importance  in  modelling  form  and 
in  its  effect  upon  the  appearances  of  colors.  Furthermore,  the 
distribution  of  light  upon  the  various  surfaces  influences  the 
mood,  spirit  or  impression  of  the  interior  as  a  whole.  The 
architect  visualizes  all  the  elements  of  which  lighting  is  an 
important  one  and  aims  to  produce  a  harmonious  blend  of 
these  in  realizing  that  result  which  he  has  held  in  his  imagina- 
tion. His  business  is  to  consult  specialists  in  all  the  sciences 
and  arts  which  he  must  draw  upon  in  producing  the  desired 
result  and  he  is  likely  to  lose  confidence  in  the  illuminating 
engineer  .if  the  latter's  view  is  confined  to  the  spacing  of  outlets 
and  to  computations  which  are  confined  to  the  supply  of  a 
certain  intensity  of  illumination  on  the  work-planes.  The 
lighting  specialist  should  be  able  to  grasp  the  imaginative 
picture  which  the  architect  has  kept  before  him  and  these  two 
should  work  in  harmony  with  the  decorator  and  other  specialists 
with  the  aim  of  obtaining  from  the  lighting  all  of  its  potential 
value.  Unfortunately  this  cooperation  is  not  as  general  as  it 
should  be  and  attention  is  focussed  upon  outlets,  fixtures  and 
lamps  without  visualizing  lighting  effects  and  striving  sufficiently 
to  obtain  them. 

In  the  industries  and  in  various  other  activities  in  which 
vision  is  severely  taxed,  the  problems  of  lighting  are  not  solved 
by  providing  a  sufficient  intensity  of  illumination  on  the  work- 
planes.  In  each  case  the  various  specific  activities  should  be 
studied  in  order  to  arrive  at  the  best  conditions  for  seeing. 
Sometimes  objects  on  which  the  eyes  are  focussed  are  best  seen 
as  high-lights  on  a  dark  ground  and  in  other  cases  as  dark  shades 
against  a  relatively  brighter  ground.  The  character  of  the 
shadows,  which  is  determined  by  the  position  and  angular 
extent  of  the  light-source  and  by  the  amount  of  scattered  light 
reflected  from  sunoundings,  is  of  importance  in  distinguishing 
objects.  The  color  of  the  surroundings,  the  spectral  character 

of  the  illuminant  and  the  environment  as  a  whole  are  factors 
2  * 


8  THE  LIGHTING  ART 

that  should  be  considered  and  controlled  by  the  lighting 
specialist  in  so  far  as  he  is  able. 

There  are  many  scientific  applications  of  color  and  colored 
light  which  are  possibilities  of  the  present  and  of  the  near 
future.  Many  of  these  will  be  touched  upon  in  chapters  which 
follow.  These  applications  involve  physical  and  chemical 
science  in  producing  colored  lights  and  effects;  they  involve 
physiological  science  in  relating  the  spectral  character  to  visual 
acuity,  to  the  intensity  of  illumination  and  to  other  factors  for 
best  results;  and  they  involve  psychological  science  through 
their  affective  value.  The  possibilities  of  color  in  lighting  are 
just  beginning  to  be  appreciated  generally  by  lighting  specialists 
but  it  is  certain  that  these  are  very  extensive. 

As  an  element  of  safety,  the  lighting  specialist  finds  much 
of  value  in  lighting.  Darkness  and  improper  lighting  are 
sources  of  danger  and  they  are  aides  to  criminals.  Proper 
lighting  not  only  conserves  human  resources  but  lessens  the 
cost  of  maintenance  of  order  in  the  community.  To  summarize 
the  value  and  importance  of  proper  lighting  as  an  element  of 
safety  would  be  an  insurmountable  task  but  there  are  sufficient 
data  to  show  that  this  is  an  aspect  of  lighting  worthy  of  con- 
sideration. It  should  be  the  lighting  expert's  function  to 
study  and  to  rectify  the  many  misuses  of  light  such  as  insuffi- 
cient lighting  in  dangerous  places,  the  blinding  effect  of  glaring 
light-sources  amid  crowded  industrial  plants  and  on  the  public 
highways,  the  proper  illumination  of  danger  signals,  etc.,  all 
of  which  have  extensive  ramifications  into  various  sciences. 
Another  important  view  in  this  connection  is  the  matter  of 
lighting  legislation  in  controlling  the  lighting  of  highways, 
public  buildings,  and  parks,  and  the  headlamps  and  rearlamps 
of  vehicles. 

Many  other  aspects  of  lighting  might  be  discussed  but  the 
foregoing  is  perhaps  sufficient  to  indicate  the  extensive  im- 
portance of  the  subject.  The  attention  given  to  lighting  and 
the  recognition  of  the  lighting  specialist  are  at  present  insig- 
nificant in  comparison  with  the  importance  of  lighting  in  human 
activities.  This  new  science  and  art  is  young  because  it  had 
small  opportunity  to  develop  until  the  advent  of  modern 


THE  BROAD  ASPECT  OF  LIGHTING  9 

illuminants.  However,  the  past  10  years  have  witnessed 
tremendous  growth  in  our  knowledge  and  application  of  light- 
ing. Much  data  remain  to  be  unearthed  but  at  least  the  light- 
ing specialist  is  certain  of  his  position  and  has  begun  the  attack 
inspired  by  the  conviction  that  lighting  is  a  factor  in  industrial 
and  commercial  development  and  in  prevention  and  safety; 
that  it  is  not  only  an  important  economic  factor  but  has  great 
possibilities  in  adding  to  the  pleasures  of  life.  The  entire 
subject  cannot  be  covered  in  a  single  volume  but  it  is  hoped  that 
in  the  following  chapters  new  viewpoints  and  new  possibilities 
will  be  presented.  It  is  the  intention  to  avoid  treating  aspects 
that  are  commonly  discussed  and  regarding  which  data  are 
readily  obtainable  from  manufacturers.  In  so  far  as  it  appears 
practicable,  discussions  of  specific  installations  will  be  sacrificed 
for  discussions  of  principles  for  the  reason  that  progress  is 
made  largely  by  those  who  are  interested  in  why  rather  than  in 
how.  Present  practice  is  bound  to  change  and  an  interest 
confined  entirely  to  this  aspect  results  in  imitation;  principles 
are  in  general  everlasting  and  interest  in  them  leads  to  creative 
ability. 


CHAPTER  II 
EXPRESSIVE  POSSIBILITIES  OF  LIGHT 

Nearly  all  problems  of  lighting  may  be  considered  as  being 
divisible  into  two  parts,  namely,  the  purely  utilitarian  and  the 
esthetic  aspects,  though  as  stated  in  the  preceding  chapter 
these  are  not  completely  separable  and  therefore  no  definite 
boundary  exists  between  them.  However,  there  is  an  ad- 
vantage in  lighting  practise  to  separate  these  two  aspects  in 
so  far  as  it  is  possible  in  the  consideration  and  design  of  the 
installation. 

In  viewing  lighting  from  the  psychological  and  esthetic  stand- 
points it  is  inspiring  to  note  that  no  medium  exists  which 
possesses  the  expressive  possibilities  of  light.  The  landscape 
artist  who  has  striven  to  paint  one  of  Nature's  scenes  with  pig- 
ments may  best  appreciate  this  statement  for  with  his  pig- 
ments of  extreme  limitations  in  range  of  contrast  and  in  purity 
of  color,  he  strives  in  vain  to  record  Nature's  expression  of 
light.  Nature  not  only  paints  her  landscapes  with  pigments 
but  utilizes  light  as  well.  The  latter  might  well  be  termed 
"primary"  light  to  distinguish  it  from  the  reflected  lights  from 
the  pigments  in  earth,  foliage,  etc.  The  painter,  with  brush 
dipped  in  terrestial  pigments,  is  seriously  handicapped  for  the 
reason  that  his  media,  under  equal  intensities  of  illumination, 
can  only  feebly  represent  that  which  is  present  in  a  landscape. 
His  pigments  under  this  condition  represent  a  maximum  range 
of  contrast  of  about  30  to  i;  that  is,  the  whitest  pigment  is 
about  30  times  brighter  than  the  blackest  pigment  under  equal 
intensities  of  illumination.  However,  the  sun  is  millions  of 
times  brighter  than  some  objects  which  it  illuminates  and  the 
sky  is  many  thousand  times  brighter  than  the  deepest  shadow. 
But  the  lighting  specialist  who  paints  with  light  can  augment 
these  contrasts  as  much  as  desired  by  controlling  the  bright- 
ness of  the  various  parts,  that  is,  by  properly  distributing  the 

illumination. 

10 


EXPRESSIVE  POSSIBILITIES  OF  LIGHT  11 

In  the  matter  of  purity  of  colors  the  painter  is  not  handi- 
capped to  such  an  extent  in  imitating  the  landscape  because  the 
colors  of  Nature  are  laigely  his  pigments.  But  here  again  arti- 
ficial lighting  may  excel  the  painter  because  it  is  possible  to 
obtain  approximately  pure  hues  and  even  the  pure  hues  of  the 
spectrum  if  necessary.  The  latter  is  not  a  requirement  of 
ordinary  lighting  but  nevertheless  it  is  a  potential  possibility 
which  may  find  a  field  of  usefulness  eventually.  The  specialist 
who  deals  with  light  should  at  least  be  familiar  with  the 
potentiality  of  his  medium. 

The  foregoing  is  an  extreme  illustration  but  there  are  many 
practical  cases  in  which  light  is  overwhelmingly  superior  to 
other  media  in  its  expressive  possibilities.  In  other  words, 
there  is  one  aspect  of  lighting  which  can  be  described  best  as 
"painting  with  light."  The  decorator  employs  pigments  in 
paints,  wall-paper,  and  cloth  fabrics  to  create  a  certain  expres- 
sion, apparently  rarely  employing  lighting  designedly  in  this 
connection.  But  the  lighting  specialist  can  do  much  to  en- 
hance the  intended  expression  or  toward  defeating  it.  Suppose 
the  decorative  scheme  in  a  given  room  to  consist  in  general 
of  grays  of  a  "cool"  or  bluish  tint,  with  the  lighter  shade  on  the 
ceiling  and  frieze  and  a  slightly  darker  giay  on  the  walls. 
Doubtless  the  grays  have  been  chosen  and  applied  under  day- 
light illumination  and  the  decorator  does  not  always  realize 
that  the  color  and  the  distribution  of  light  are  playing  parts  in 
the  effect  obtained.  Daylight  usually  enters  rooms  from  side 
windows  and  rarely  are  the  amounts  of  light  admitted  from  the 
various  sides  equal  in  intensity.  Furthermore,  the  illumination 
is  usually  more  intense  on  the  floor  than  on  the  ceiling.  It  is 
obvious  that  with  common  artificial  lighting  systems  the  dis- 
tribution of  light  will  be  different  and  consequently  the  decora- 
tive scheme  will  be  differently  balanced.  Incidentally  the 
distribution  of  illumination  from  an  ordinary  direct-lighting 
system  with  pendant  shades  more  generally  simulates  daylight 
distribution  indoors  than  does  the  distribution  of  illumination 
from  an  indirect-lighting  system.  Under  the  artificial  illumi- 
nants  the  cool  grays  usually  change  to  warm  grays  which 
further  emphasizes  the  expressive  power  of  lighting.  If  the 


12  THE  LIGHTING  ART 

grays  are  of  a  decided  bluish  tint  their  conversion  to  warm  grays 
may  perhaps  be  unattained  without  tinting  the  illuminant  to  the 
warmer  color  of  the  candle  flame  or  even  a  deeper  yellow.  This 
is  readily  done  by  various  means  as  will  be  discussed  later. 
Such  an  application  of  tinted  light  changes  very  materially  the 
impression  of  the  room  as  a  whole. 

The  expressive  possibilities  of  lighting  find  extensive  applica- 
tion in  relation  to  architecture.  Aside  from  the  modelling  of 
ornament,  the  light  and  shade  effects  of  relatively  large  areas 
such  as  walls  and  ceiling,  the  contrasts  in  the  brightnesses  of 
alcoves  with  that  of  the  main  interior,  and  the  shadows  under- 
neath ceiling  beams  are  all  expressions  of  light.  These  create 
certain  moods  appropriate  or  inappropriate  depending  upon 
the  spirit  of  the  whole  interior.  When  an  expanse  of  ceil- 
ing is  apparently  supported  by  beams,  a  dark  shade  on  the  under 
side  of  the  beams  completes  the  illusion  of  supporting  ability. 
This  illusion  is  best  obtained  by  lighting  because  if  it  were 
created  by  the  decorator  doubtless  under  ordinary  daylighting 
which  is  less  easily  controllable  in  distribution,  the  artifice 
would  be  evident  because  the  lower  sides  of  the  beams  would 
appear  to  be  finished  a  darker  shade. 

A  large  interior  of  beautiful  architectural  proportions  may  be 
given  a  variety  of  moods  by  means  of  various  appropriate 
distributions  of  light.  When  flooded  with  light  from  indirect 
units  hung  from  the  ceiling  it  has  the  airiness  and  extensive- 
ness  of  outdoors.  When  lighted  by  means  of  units  concealed 
in  the  upper  cornice  the  ceiling  will  be  bright  and  the  walls  are 
likely  to  be  moderately  dark  by  contrast.  The  feeling  of  being 
hemmed  in  by  the  walls  and  the  illusion  of  an  open  roof  above 
is  not  uncommon  under  such  lighting.  When  lighted  by  means 
of  low-hung  chandeliers  which  direct  much  of  the  light  down- 
ward, the  ceiling  and  walls  are  likely  to  be  moderately  dark  by 
contrast  and  if  these  are  decorated  with  a  medium  shade  the 
illusion  is  likely  to  be  that  of  being  hemmed  in  by  the  moderate 
darkness  of  the  surroundings.  Thus  lighting  is  productive  of 
illusions  ranging  from  the  mystery  of  crowding  darkness  to  the 
extensiveness  of  outdoors.  In  such  classes  of  architectural 
interiors  the  possibilities  of  lighting  perhaps  far  exceed  those 


EXPRESSIVE  POSSIBILITIES  OF  LIGHT  13 

of  decoration  though  as  yet  lighting  has  not  taken  its  place 
even  by  the  side  of  decoration  as  a  recognized  art. 

To  these  possibilities  and  many  more,  the  expressive  possi- 
bilities of  colored  light,  especially  of  the  tints  or  extremely  un- 
saturated  colors,  may  be  added.  The  expressiveness  of  tinted 
light  is  well  displayed  in  the  home.  The  warm  colors  of  the 
old  illuminants  such  as  the  candle  and  kerosene  flames  may 
be  obtained  readily  from  modern  illuminants  by  the  aid  of 
colored  media.  The  future  will  witness  developments  along 
this  line  which  will  make  it  easy  to  obtain  the  desired  effects. 
There  are  many  possibilities  in  applying  colored  illuminants 
of  artistic  tints  to  the  decorative  scheme,  permanently  or  for 
various  special  functions.  The  tints  which  are  applicable  run 
the  whole  gamut  of  the  spectrum  in  hue  and  include  the  pinks 
or  rose  tints.  How  such  tinted  illuminants  fit  the  spirit  of  an 
occasion  or  the  mood  of  a  room  may  be  appreciated  only  through 
experiment.  Tints  that  are  especially  appropriate  are  warm 
yellow,  rose,  unsaturated  green,  and  even  light  blues. 

In  such  interiors  as  lounging  rooms  of  clubs  and  hotels,  living 
rooms,  dining  rooms,  dens,  and  ball  rooms,  two  or  three  different 
tints  may  be  employed.  A  general  soft  illumination  of  a  warm 
tint  might  be  chosen  but  this  may  be  effectually  emphasized 
here  and  there  by  contrasting  tints  in  portable  lamps  or  bracket 
fixtures.  Deeper  tints  of  that  used  for  general  illumination 
may  be  employed  sometimes  for  emphasis  with  good  effect. 
However,  there  is  a  principle  to  be  remembered  in  dealing  with 
colored  illuminants  for  their  expressive  value,  namely,  that 
colors  live  through  contrast  and  die  through  lack  of  it.  To  take 
an  extreme  case,  for  example  assume  a  room  lighted  with  satu- 
rated red  light.  As  the  time  of  adaptation  increases  the  purity 
of  the  red  apparently  disappears  and  the  appearance  of  the 
whole  room  is  that  of  a  monochrome  in  an  unsaturated  orange. 
Even  the  red  objects  lose  their  purity  of  hue  and  such  applica- 
tions have  little  value  except  for  psychological  studies.  Now 
inject  into  this  monochrome  a  spot  of  light  of  any  other  color 
and  the  red  bursts  forth  in  all  its  purity  of  color.  Contrast 
is  essential  to  the  life  of  colors. 

A  case  less  extreme  and  more  endurable  is  to  employ  a  deep 


14  THE  LIGHTING  ART 

yellow  illuminant.  Many  colors  about  the  room  disappear 
and  the  few  remaining  such  as  green,  yellow,  orange  and  red 
are  crowded  together.  Place  such  an  illuminant  over  the  dining 
table  and,  for  example,  the  butter  is  no  longer  appealing  for 
it  might  be  readily  mistaken  for  lard.  This  experiment  will 
dispel  the  mistaken  opinion  that  yellow  light  brings  out  the 
yellow  colors.  In  fact  it  drowns  out  the  yellows  for  there  are 
no  striking  contrasts  to  keep  the  colors  alive.  The  same  dis- 
cussion applies  to  any  illuminant  that  approaches  mono- 
chromatism  in  spectral  character. 

Among  the  many  installations  of  artificial  daylight  are  found 
striking  examples  of  the  expressive  powers  of  the  color  and  of  the 
distribution  of  light.  In  a  large  art  museum  where  the  artificial 
daylight  units  are  concealed  above  the  sub-skylight,  the  effect 
is  so  similar  to  daylight  and  the  illusion  so  powerful  that  it  is 
difficult  to  believe  night  has  fallen.  This  example  affords  proof 
of  the  necessity  of  coordinating  both  distribution  and  spectral 
character  of  the  illuminant  for  obtaining  the  effect.  To  the 
careful  observer  even  this  illusion  is  not  perfect  because  of  the 
symmetrical  distribution  of  the  artificial  light,  a  condition 
rarely  obtained  with  natural  light  except  on  overcast  days. 
Those  who  study  Nature's  lighting  are  impressed  with  the 
directedness  of  the  light  except  on  densely  overcast  days.  A 
knowledge  of  such  details  is  essential  in  order  to  employ  the 
expressive  power  of  light  to  the  limit  of  its  possibilities. 

To  summarize  the  foregoing  viewpoint  in  the  most  descriptive 
phrase  it  may  be  stated  that  the  lighting- artist  may  "  paint  with 
light."  The  decorator  and  painter  utilize  light,  shade,  and  color 
for  their  work  but  their  tools  are  pigments,  brushes,  etc.  Light 
and  its  accessories  provide  superior  possibilities  in  obtaining 
beautiful  effects.  Quite  the  same  esthetic  principles  are  in- 
volved in  this  aspect  of  lighting,  and  artistic  skill  may  utilize 
light  in  a  vast  variety  of  ways  in  the  same  interior  thus  produc- 
ing various  moods.  The  walls,  ceiling  and  other  areas  are  the 
canvases  for  light,  shade,  and  color  effects  in  lighting  and  the 
objects  in  the  room  provide  real  shadows.  In  a  sense  this 
aspect  of  lighting  involves  the  combined  principles  of  painting, 
decoration,  sculpture,  and  architecture.  Lighting  fixtures  and 


EXPRESSIVE  POSSIBILITIES  OF  LIGHT  15 

outlets  of  the  future  will  likely  provide  for  these  possibilities 
to  a  much  greater  extent  than  they  do  at  present  as  the  psycho- 
logical and  decorative  aspects  of  lighting  become  more  widely 
known  and  applicable  and  as  the  pleasures  from  variety  in 
lighting  become  recognized. 


CHAPTER  III 
VISUALIZATION 

To  state  that  visualizing  a  desired  effect  in  lighting  is  the 
surest  means  of  ultimately  realizing  the  contemplated  goal  is 
merely  to  enunciate  a  corollary  to  the  more  general  statement 
that  imagination  is  the  source  of  creative  efforts.  The  ability 
to  visualize  is  especially  essential  in  approaching  lighting 
problems  in  which  the  artistic  aspect  dominates,  but  it  must  be 
present  in  approaching  any  lighting  problem.  First,  it  is  neces- 
sary to  separate  illumination  and  brightness  which  are  re- 
spectively cause  and  effect.  Illumination  is  independent  of 
the  surface  at  which  it  is  measured  but  brightness  depends 
upon  the  reflection-factor  and  character  of  the  surface.  Visual- 
izing the  effect  of  a  lighting  installation  in  terms  of  the  illumina- 
tion which  it  is  expected  to  supply  on  various  work-planes  is 
not  visualizing  the  actual  lighting  effects  for  the  latter  involve 
relative  brightnesses  and  colors  and  their  distributions. 

Furthermore,  lighting  when  done  by  considering  only  illu- 
mination is  in  general  neither  scientific  nor  artistic.  The  ac- 
tivities which  are  to  be  pursued  at  various  points  in  the  room 
should  be  considered  and  an  attempt  should  be  made  to  visualize 
the  process  of  seeing  in  each  case.  Backgrounds  against  which 
the  work  is  viewed  are  often  of  as  much  importance  as  the 
intensity  of  illumination.  Lighting  should  have  the  aim  of 
providing  good  seeing  if  this  is  essential  and  the  visualizing 
ability  is  taxed  in  such  a  case  as  well  as  in  producing  artistic 
results  where  these  are  important.  Lighting  has  not  been 
developed  to  an  exact  science  in  its  brief  existence  as  a  special- 
ized activity  so  that  it  is  quite  legitimate  to  resort  to  experi- 
mental installations  when  possible;  however,  the  necessity  for 
such  procedure  decreases  as  the  lighting  specialist  acquires 
knowledge  of  optical  laws,  lighting  effects,  optical  characteristics 
of  surfaces,  effects  of  surroundings,  etc.,  or  in  other  words 
develops  his  ability  to  visualize  results. 

16 


VISUALIZATION  17 

/ 

This  view  of  lighting  practice  emphasizes  the  folly  of  attempt- 
ing to  plan  lighting  appropriate  to  a  setting  from  blueprints 
alone.  In  order  to  do  justice  to  the  possibilities  of  lighting  and 
to  himself,  the  lighting  specialist  should  be  familiar  with  the 
architectural  details,  with  the  decorative  ornaments,  with  the 
entire  scheme  of  decoration  as  to  colors  and  brightness  distribu- 
tion and  with  the  intended  spirit  of  the  finished  work. 

Visualization  is  utilized  to  some  extent  in  all  work  but  this 
faculty  must  be  highly  developed  before  lighting  practitioners 
evolve  into  lighting  experts.  This  ability  well  developed  is  one 
of  the  characteristics  which  distinguish  the  lighting  specialist 
or  expert  from  the  illuminating  engineer,  the  meaning  of  the 
latter  term  being  taken  literally.  The  lighting  expert,  by 
becoming  fully  acquainted  with  the  many  aspects  of  light  and 
its  uses,  by  cultivating  his  esthetic  sense,  and  by  developing 
his  power  of  imagination  or  ability  to  visualize,  has  fitted  him- 
self for  his  title  because  he  is  now  capable  of  viewing  the  prob- 
lems of  lighting  from  that  broad  viewpoint  which  is  bounded 
only  by  the  limits  of  human  activities. 

In  order  to  visualize  in  lighting  it  is  necessary  to  know  the 
simple  optical  laws;  to  be  familiar  with  the  optical  characteris- 
tics of  various  kinds  of  reflecting  and  transmitting  media;  to 
be  able  to  form  a  general  idea  of  the  brightnesses  of  the  various 
surrounding  areas  under  the  different  intensities  of  illumination 
which  they  will  receive;  to  be  familiar  with  the  purpose  of  the 
lighting,  the  aim  of  the  architect,  and  the  plans  of  the  decorator; 
and  in  general  to  be  able  to  relate  in  the  mind's  eye  the  distribu- 
tions of  brightness  and  of  color  to  the  character  of  the  activity 
and  to  the  mood  or  expression  which  it  is  the  aim  to  realize. 
Armed  with  this  aggregate  ability  the  lighting  expert  is  prepared 
to  begin  the  plans  for  a  lighting  installation  with  his  eyes 
closed  and  his  mind's  eye  open. 

In  order  to  further  exemplify  the  importance  of  visualiza- 
tion in  lighting  and  what  is  to  be  visualized  let  us  inquire 
further  into  the  process  of  seeing.  The  analysis  of  human 
consciousness  reveals  two  kinds  of  visual  sensations,  namely, 
chromatic  and  achromatic  sensations.  No  masterpiece  of 
painted  or  sculptured  art,  no  beautiful  landscape,  no  office  or 


18  THE  LIGHTING  ART 

factory  operation  and  no  lighting  effect,  so  far  as  the  visual 
sense  is  concerned,  consists  of  more  than  an  arrangement  or 
sequence  of  varied  colors  and  brightnesses.  In  other  words 
vision  is  accomplished  through  the  ability  to  distinguish  dif- 
ferences in  light,  shade,  and  color.  If  the  image  of  any  scene 
which  is  focussed  upon  the  retina  could  be  examined,  it  would 
appear  as  a  miniature  map  of  varied  colors  and  brightnesses 
similar  to  that  seen  on  the  focussing  screen  of  a  camera.  How- 
ever, in  the  case  of  the  eye  only  that  part  of  the  image  which 
is  near  the  optical  axis  is  in  true  focus  and  the  differences 
between  the  two  records  are  further  accentuated  by  the  presence 
of  physiological  and  psychological  phenomena  in  the  human 
visual  process.  In  fact,  the  latter  are  the  vast  unknowns  in 
lighting. 

It  is  not  generally  enough  recognized  that  the  fundamentals 
of  lighting  are  light,  shade,  and  color  effects  for  it  is  the  varia- 
tion of  these  factors  which  models  and  paints  an  object  or  an 
interior.  No  appreciable  ability  to  visualize  lighting  effects 
can  be  developed  without  a  painstaking  study  of  light,  shade, 
and  color  as  related  to  the  appearances  of  objects,  to  the  physio- 
logical processes  involved  in  vision  and  to  the  psychological 
phenomena  associated  with  visual  impressions.  In  other  words, 
the  expressiveness  and  revealing  power  of  lighting  are  wholly 
dependent  upon  distributions  of  brightness  and  of  color. 

It  should  be  easy  to  develop  an  ability  to  visualize  lighting 
effects  because  demonstrations  are  everywhere  awaiting  the 
observer.  The  importance  of  color  is  omnipresent  in  the 
magical  drapery  in  nearly  all  the  scenes  about  us  and  the 
importance  of  high-lights  and  shadows  and  of  the  varied  bright- 
nesses of  relative  large  areas  may  be  studied  everywhere  in 
objects,  landscapes,  and  interiors.  Hence,  it  is  helpful  in  de- 
veloping the  ability  to  visualize  to  divide  lighting  and  its  im- 
pressions into  two  parts,  namely,  that  which  depends  upon  the 
distribution  of  light  and  that  which  depends  upon  the  quality 
of  light. 

The  importance  of  visualization  should  be  obvious  after 
some  consideration  and  the  proof  of  this  can  be  safely  left  to 
the  reader.  In  fact,  it  is  difficult  to  describe  without  the  use 


VISUALIZATION  19 

of  actual  demonstrations.  Observation  is  the  best  means  of 
investigating  the  importance  of  visualization  but  perhaps  a 
few  comments  on  specific  cases  may  aid  in  helping  those  desir- 
ing proof  to  make  their  own  observations.  Let  us  take  any 
ornamental  interior  where  the  architectural  patterns  are  sym- 
metrically distributed.  If  the  whole  is  not  to  be  uniformly 
lighted  the  problem  of  properly  distributing  the  light  is  diffi- 
cult because  the  various  brightnesses  often  should  conform  to 
various  individual  areas,  panels,  or  other  patterns.  Although 
in  some  cases  a  fairly  uniform  flood  of  light  is  appropriate,  a 
decided  lack  of  uniform  brightness  due  to  lighting  is  most 
generally  conducive  to  artistic  results.  In  such  an  interior 
the  decorator  almost  invariably  confines  his  different  bright- 
ness boundaries  to  boundaries  of  patterns.  But  seldom,  if 
ever,  is  the  distribution  of  light  confined  to  uniformity  over  a 
definite  portion  of  the  pattern  bounded  by  architectural 
boundaries.  To  distribute  light  with  exactitude  in  this  manner 
is  beyond  practicable  possibility  because  it  would  involve  a 
fineness  of  control  of  light  quite  without  the  bounds  of  reason. 
However,  this  insurmountable  difficulty  does  not  justify  the 
lighting  specialist  in  making  no  attempt  to  obtain  lighting 
accessories  which  will  distribute  the  light  in  such  a  manner 
upon  the  various  surfaces  so  that  there  is  a  more  than  accidental 
relation  between  lighting  effects  and  decorative  patterns.  Here 
the  ability  to  visualize  is  of  value  for  it  should  result  in  a  choice 
of  suitable  lighting  units,  a  selection  of  the  proper  places  for 
outlets,  and  a  satisfactory  mounting  height  of  units.  Some- 
times designs  of  lighting  units  which  are  simple  but  uncommon 
may  overcome  the  difficulty.  A  spotted  and  haphazard  light- 
ing effect  may  be  avoided  and  lighting  effects  appropriate  to 
the  decorative  patterns  may  be  obtained.  Only  visualization 
•will  lead  to  such  designs. 

In  planning  a  decorative  scheme  in  the  home,  satisfactory 
results  will  be  obtained  only  by  maintaining  in  the  mind's  eye 
a  picture  of  the  desired  result  and  by  linking  one  by  one  the 
various  elements  of  the  whole.  Lighting  plays  its  part  in  this 
scheme  and  the  choice  of  various  types  of  direct  lighting,  of  in- 
direct and  of  so-called  semi-indirect  lighting  must  be  made 


20  THE  LIGHTING  ART 

early  in  the  plans  if  a  harmonious  result  is  to  be  made  certain. 
Here  visualization  is  the  definite  means,  aside  from  actual 
experiment,  for  determining  the  character  of  the  installation 
and  whether  or  not  the  artistic  possibilities  of  asymmetrical 
lighting  from  portable  units  can  be  utilized. 

Another  case  which  may  aid  in  suggesting  studies  of  visualiza- 
tion is  that  of  a  beautiful  architectural  interior  having  high 
vaulted  arches,  columns,  etc. ,  such  as  a  church.  Certainly  mood 
is  a  prominent  factor  in  such  a  setting.  A  choice  of  an  indirect 
system  of  lighting  from  suspended  units  or  from  sources  con- 
cealed behind  a  cove,  or  of  chandeliers,  or  of  other  systems 
must  necessarily  be  the  result  of  visualizing  the  appropriate 
lighting  effect  and  of  adapting  the  installation  to  it.  A  flood 
of  light  from  concealed  sources  upon  an  expanse  of  high  ceiling 
is  just  as  appropriate  in  some  churches  as  contrasty  light  and 
shade  effects  or  dark  ceilings  are  in  others  depending  upon 
the  character  of  the  architecture  and  somewhat  upon  the 
denomination. 

This  brief  discussion  and  these  few  examples  should  be  suffi- 
cient to  indicate  the  importance  of  visualization  in  lighting. 
This  aspect  of  a  lighting  problem  which  should  be  one  of  the 
first  steps  taken  in  the  consideration  of  a  lighting  plan  is 
certainly  much  neglected  or  underestimated  in  value — a  fact 
which  may  be  readily  proved  by  observing  some  of  the  methods 
of  attacking  and  of  solving  lighting  problems.  It  is  not  always 
neglected  and  in  those  cases  where  the  value  of  visualization  is 
utilized,  the  results  are  satisfactory  testimonials  of  this  value. 
Imagination  and  a  knowledge  of  the  scientific  and  artistic 
aspects  of  lighting  is  the  combination  which  results  in  creative 
lighting. 


CHAPTER  IV 
VARIETY— THE  SPICE  OF  LIGHTING 

Many  observations  and  experiments  have  led  the  author  to 
subscribe  to  the  parodical  title  of  this  brief  chapter.  We  de- 
mand patterns  or  texture  in  wall-paper,  rugs,  and  upholstery, 
variation  in  light,  shade,  and  color  in  the  decorative  scheme  of 
an  interior,  ornamental  architecture  indoors  and  outdoors, 
frequent  changes  in  the  arrangement  of  furniture,  and  in  many 
other  ways  express  the  human  craving  for  change.  Variety 
is  one  of  the  vital  necessities  for  human  endurance  and  even  for 
existence.  How  strange  it  is  that  this  innate  demand  for 
variety  has  not  extended  more  definitely  to  lighting  for,  with 
comparatively  simple  expedients,  no  other  source  is  so  produc- 
tive of  variety.  A  few  extra  outlets  for  portable  lamps,  simple 
combinations  of  lighting  principles  in  portable  lamps  and  in 
suspended  fixtures,  two-  and  three-circuit  fixtures  each  pro- 
viding light  of  different  distribution  and  possibly  of  different 
tint  are  possibilities  for  obtaining  a  distribution  and  color  of 
light  to  suit  the  mood  or  the  occasion.  However,  the  provisions 
for  obtaining  variety  in  lighting  seldom  extend  beyond  a  two- 
circuit  unit  providing  only  a  possibility  of  varying  the  intensity 
of  light,  and  a  few  connections  for  portable  lamps,  although 
simple  combinations  of  accessories  and  of  multiple  circuits  are 
sources  of  this  most  appealing  feature  of  lighting. 

Of  all  lighting  systems,  Nature's  lighting  is  the  least  monoton- 
ous and  a  study  of  it  leads  to  the  conclusion  that  this  is  due 
largely  to  the  perpetual  change  in  distribution  and  color  of 
light.  When  Nature's  lighting  is  restricted  in  distribution  and 
color  as  it  is  indoors  by  the  artificial  shackles  constructed  by 
man,  its  variety  is  suppressed  and  it  often  becomes  monotonous 
and  unsatisfactory.  However,  in  the  great  outdoors,  where 
Nature  is  unhampered,  the  lighting  varies  continually  through- 
out a  given  day,  as  well  as  from  day  to  day  and  from  season  to 

21 


22  THE  LIGHTING  ART 

season.  It  presents  the  extremes  of  variation  in  light-distribu- 
tion on  overcast  and  sunny  days  respectively  and  in  the  latter 
cases  the  shadows  are  continually  shifting  with  the  sun's  alti- 
tude. The  color  aspect  varies  throughout  the  day  from  sunrise 
to  sunset  and  no  sunrise,  sunset,  or  landscape  ever  presents 
identical  appearances  at  different  times. 

If  a  certain  landscape  be  studied  throughout  the  day  usually  it 
will  be  found  to  be  most  interesting  and  enticing  during  early 
morning  and  late  afternoon  on  a  clear  day  because  of  the  pres- 
ence of  variety  due  to  long  shadows.  Nature's  scenes  lose 
much  of  their  appeal  on  overcast  days  when  there  is  less  variety 
of  light,  shade,  and  color.  Incidentally,  Nature  provides  ex- 
cellent opportunities  for  studying  this  aspect  of  lighting  and 
others  because  a  vast  array  of  different  distributions  of  light 
are  present  on  every  hand.  The  variations  in  the  brightness 
and  color  of  a  landscape  and  in  the  distribution  of  light  owing  to 
intercepting  foliage  provide  many  studies  in  lighting  effects. 

Variety  in  lighting  not  only  includes  the  different  distribu- 
tions of  light  and  color  attainable  by  the  lighting  equipment 
primarily  but  also  the  variety  in  the  distribution  of  light,  shade 
and  color  in  a  given  case.  In  many  interiors,  symmetry  is  a 
keynote  and  in  such  cases,  symmetrical  lighting  effects  harmon- 
ize with  the  whole.  But  in  most  interiors,  such  .as  living  rooms, 
restaurants,  and  lounging  rooms,  symmetrical  lighting  effects 
are  unnecessary  and  are  often  monotonous,  inartistic  and  even 
obtrusive.  For  example,  let  us  take  the  case  of  a  living  room 
which  is  occupied  for  long  periods  nightly.  To  one  possessing 
a  fine  sensibility  it  is  extremely  monotonous  to  be  greeted  with 
the  same  symmetrical  distribution  of  light  from  the  ordinary 
central  fixture.  If  two  circuits  are  provided  for  this  fixture  a 
slight  relief  is  available  by  variety  in  intensity  especially  if  un- 
balanced by  the  light  from  a  library  lamp  asymmetrically 
located.  If  fixtures  are  provided  with  accessories  which  make  it 
possible  to  obtain  two  widely  different  distributions  of  light,  it 
becomes  possible  to  provide  a  lighting  more  in  sympathy  with  the 
mood  and  thus  to  relieve  the  monotony  to  some  extent.  Table 
lamps  and  brackets  lend  variety  which  pleases  the  finer  sensi- 
bilities and  aid  much  in  providing  means  for  adapting  the 


VARIETY—THE  SPICE  OF  LIGHTING  23 

lighting  of  the  room  to  the  mood  or  to  the  occasion.  In  fact, 
it  will  not  be  surprising  to  find  that  central  lighting  fixtures  in 
such  rooms  will  be  less  used  as  the  possibilities  of  variety  in 
light,  shade,  and  color  in  a  given  lighting  effect  and  of  a  variety 
of  different  lighting  effects  become  more  appreciated. 

However,  symmetry  in  distribution  of  light  is  appropriate  in 
such  a  case  as  the  dining  room  where  necessity  demands  it  and 
the  setting  would  be  incomplete  without  it.  However,  even 
in  the  dining  room  there  is  much  pleasure  to  be  obtained  from 
a  ceritral  fixture  which  provides  different  distributions  of  light 
and  the  possibility  of  introducing  tinted  light  when  desired.' 

On  viewing  an  art  exhibition  with  a  great  artist  where  day- 
light quality  of  light  had  been  simulated  by  artificial  lighting 
units  placed  above  a  slightly  diffusing  skylight,  the  artist  re- 
marked that  the  quality  of  light  was  excellent  and  that  the 
light  was  evenly  distributed,  but  that  daylighting  in  a  broad 
sense  had  not  been  entirely  imitated.  Something  was  missing 
which  upon  further  discussion  proved  to  be  a  degree  of 
directedness  or  lack  of  symmetry  required  by  the  artist's  fine 
sensibility  which  had  often  communed  with  Nature.  That 
this  artist  was  correct  in  his  deduction,  which  was  arrived  at  not 
through  an  acquaintance  with  the  bare  scientific  facts  but 
through  the  impressions  which  lighting  had  made  upon  him, 
is  readily  concluded  upon  studying  Nature's  lighting.  It  is 
also  evident  that  training  in  esthetics  yields  much  of  interest 
in  lighting  even  though  the  individual  facts  are  not  laid  bare 
by  careful  analysis.  Associations  of  this  character  would  alter 
the  attitude  of  the  illuminating  engineer  who  scoffs  at  the 
esthetic  and  other  psychological  possibilities  in  lighting. 

The  magnitude  of  Nature  is  great  enough  to  play  an  impor- 
tant role  in  the  making  of  a  human  mood;  that  is,  our  moods 
often  readily  fit  themselves  into  that  of  the  natural  environ- 
ment outdoors.  We  have  all  responded  to  the  cheerfulness  of  a 
sunny  morning  and  have  been  depressed  by  the  overcast  day. 
Occasionally  if  great  sorrow  or  great  joy  is  sufficiently  intense 
even  Nature's  smile  or  frown  cannot  alter  it  but  in  general 
Nature's  mood  is  the  dominant  one.  However,  the  human 
mood  usually  desires  to  dominate  the  artificial  setting  perhaps 


24  THE  LIGHTING  ART 

because  of  the  knowledge  that  the  latter  is  artificial  and  there- 
fore may  be  altered.  For  this  reason  means  should  be  provided 
for  adjusting  the  lighting  in  harmony  with  the  mental  state  or 
with  the  spirit  of  the  occasion.  This  is  readily  possible  only 
when  such  means  are  provided,  though  rarely  is  this  factor 
considered  sufficiently. 

Lighting  units  are  appearing  on  the  market  which  are  designed 
to  satisfy  this  innate  desire  for  variety  to  a  limited  degree  at 
least.  The  so-called  direct-indirect  units  make  it  possible  to 
alter  the  distribution  from  a  concentration  of  light  in  a  small 
area  leaving  the  remainder  of  the  room  in  twilight,  to  a  flood 
of  light  over  the  entire  room  when  the  mood  or  occasion  de- 
mands it.  Portable  units  and  brackets,  asymmetrically  lo- 
cated, carry  this  idea  further  so  that  it  is  readily  possible  to 
obtain  a  harmonious  distribution  of  light,  shade,  and  color. 
There  are  a  few  fixtures  in  which  direct  units  are  combined  with 
a  semi-indirect  unit.  When  the  direct  and  semi-indirect  units 
are  placed  on  separate  circuits  some  relief  from  the  usual  monot- 
ony is  possible.  However,  such  units  are  not  in  general  use 
and  the  fault  lies  perhaps  in  the  lack  of  appreciation  of  the 
pleasures  from  variety  in  lighting  on  the  part  of  the  illuminating 
engineer,  the  fixture-  manufacturer,  the  contractor,  and  the 
consumer. 

Although  the  means  for  obtaining  variety  in  distribution  of 
light  in  present  lighting  installations  are  meager,  those  for  ob- 
taining variety  in  color  are  even  rarer.  There  is  a  demand, 
continually  growing  more  definite  and  insistent,  for  tinted 
lamps  for  the  purpose  of  obtaining  variety  in  color  in  lighting. 
The  purer  colors  may  have  fields  in  this  respect  but  artistic 
lighting  in  most  interiors  will  be  confined  to  delicate  and  barely 
perceptible  tints  which  are  more  "felt"  than  seen.  At  present 
silk  shades  are  popular  and  it  appears  that  much  of  this  popu- 
larity is  due  to  a  desire  for  tinted  light.  The  light  transmitted 
and  reflected  by  such  fabrics  is  tinted,  and  beautiful  effects 
may  be  obtained  by  applying  textile  shades  to  light-sources. 
There  is  some  tinted  glassware  available  and  units  have  been 
devised  for  quickly  altering  the  color  effect  by  changing  the 
silk  coverings  of  semi-indirect  bowls.  Colored  gelatines  and 


VARIETY—THE  SPICE  OF  LIGHTING  25 

colored  glasses  are  available  but  not  in  such  a  practicable  form 
as  to  be  readily  adaptible  to  general  interior  lighting  fixtures. 

The  greatest  possibilities  in  introducing  tinted  light  into 
interiors  lie  in  employing  colored  lamps  in  multicircuit  fixtures. 
By  mixing  these  tinted  lights  a  variety  of  tints  may  be  ob- 
tained. Although  approaching  the  theatrical,  there  are  de- 
lightful possibilities  in  using  colored  lamps  such  as  primary  red, 
green,  and  blue,  controlled  by  rheostats  which  may  be  concealed 
in  the  wall.  By  varying  these  components  of  colored  light 
any  desired  tint  may  be  obtained.  Such  an  arrangement  has 
been  used  by  concealing  the  lamps  above  a  panel  of  diffusing 
glass  set  in  the  ceiling.  This  provides  great  possibilities  in 
fitting  both  the  intensity  and  color  of  the  light  to  the  mood  or 
occasion. 

Many  other  possibilities  present  themselves  to  those  who  ap- 
preciate this  aspect  of  lighting.  An  artificial  window  covered 
with  lattice  and  foliage  may  provide  either  artificial  moonlight 
or  sunlight  as  desired.  For  example,  the  former  provides  de- 
lightfully restful  lighting  for  lounging  or  for  musical  renditions 
while  the  latter  in  congested  residential  districts  would  be  wel- 
comed very  often.  Other  devices  such  as  vases  and  imitation 
flower-boxes  on  pedestals,  on  the  mantel  or  on  the  walls  provide 
places  for  concealing  light-sources  which  at  the  proper  time  add 
pleasure  to  an  otherwise  monotonous  lighting.  One  would 
hesitate  to  attempt  to  describe  the  possibilities  in  lighting  which 
would  be  exemplified  by  a  lighting  specialist  who  was  given 
carte  blanche  while  the  plans  were  being  made  for  a  residence  in 
which  the  psychological  possibilities  of  lighting  could  be  fully 
utilized.  Some  of  the  foregoing  suggestions  may  appear  ex- 
treme and  out  of  place  in  a  discussion  of  lighting,  however,  they 
have  been  tried  with  pleasing  results.  In  general,  lighting 
will  never  attain  a  high  level  as  an  art  until  the  attention  is 
more  definitely  directed  toward  realizing  many  of  its  untried 
possibilities. 

To  summarize,  monotony  in  lighting  can  be  avoided  only  by 
providing  means  for  varying  the  distribution  and  quality  of 
light.  Fixtures  of  today  are  generally  too  simple  in  wiring  and 
design  to  give  artificial  lighting  an  opportunity  to  compete  with 


26  THE  LIGHTING  ART 

Nature's  lighting  outdoors  in  gaining  the  favor  of  the  finer 
human  sensibilities.  The  advent  of  a  few  lighting  units  de- 
signed to  furnish  a  degree  of  variety  of  light,  shade,  and  color 
is  perhaps  an  indication  of  economic  and  esthetic  demands,  but 
progress  in  this  direction  has  barely  begun.  It  is  believed, 
when  the  full  import  of  variety  in  lighting  has  become  appreci- 
ated by  lighting  specialists,  fixture  designers,  contractors,  and 
consumers,  the  procedure  of  lighting  many  classes  of  interiors 
will  be  altered  considerably  and  that  lighting  fixtures  and  tinted 
lamps  adaptable  for  providing  this  variety  will  be  more  gener- 
ally available.  This  aspect  will  crop  out  occasionally  in  other 
chapters. 

In  closing  this  chapter,  which  treats  an  aspect  of  lighting 
possessing  vast  potentiality,  we  might  summarize  in  a  few  words 
appropriate  to  lighting  as  well  as  to  life.  Variety  leads  us 
happily  through  a  colorful  sojourn;  monotony  condemns  us 
to  a  colorless  existence.  Monotony  is  a  monochrome  and,  true 
to  the  laws  of  color,  it  loses  its  color  through  continued  adapta- 
tion. Variety  is  a  mobile  painting  in  light,  shade,  and  color 
done  by  a  master  colorist,  and  it  provides  perpetual  interest  as 
it  is  altered  to  suit  our  mood  or  fancy.  In  thinking  of  variety 
in  lighting  the  metaphorical  phrase,  " painting  with  light" 
seems  most  appropriate. 


CHAPTER  V 
DISTRIBUTION  OF  LIGHT 

The  preliminary  steps  in  any  analysis  aim  to  subdivide  the 
problem  into  a  few  broad  aspects  and  later  to  assume  various 
viewpoints  in  considering  these.  In  lighting  it  is  often  ad- 
vantageous to  divide  problems  of  planning  or  of  analyzing 
lighting  effects  into  two  broad  though  interwoven  parts, 
^namely,  distribution  and  quality  of  light.  To  describe  all  the 
ramifications  of  either  of  these  factors  would  be  a  task  whose 
record  would  greatly  overflow  the  confines  of  a  single  volume, 
but  chief  features  of  these  two  interwoven  aspects  form  the 
major  part  of  the  discussions  recorded  in  this  book.  One  ad- 
vantage of  this  division  is  that  the  effects  of  color  are  separated 
from  those  of  distribution  of  light.  In  other  words,  the  latter 
aspect  would  constitute  the  entire  consideration  of  lighting  by 
a  color-blind  person.  It  involves  much  more  than  the  distribu- 
tion of  light  as  emitted  by  light-sources  and  controlled  by  re- 
flectors, shades  and  other  accessories,  for  it  includes  the  dis- 
tribution of  illumination  and  brightness  upon  the  various  areas 
such  as  walls  and  ceiling,  the  formation  of  shadows,  and  many 
other  factors. 

For  the  consideration  of  the  distribution  of  light  from  light- 
sources  and  their  equipment,  engineers  and  scientists  have 
supplied  excellent  data  and  this  aspect  of  lighting  has  been 
highly  developed.  Light-sources  have  been  modified  in  char- 
acter in  many  ways  which  adapt  them  to  the  many  require- 
ments of  lighting  and  a  great  many  accessories  have  been  de- 
signed for  the  purpose  of  obtaining  various  distributions  of 
light  for  the  rapidly  growing  demands.  As  a  consequence, 
lighting  units  are  available  for  highly  diffusing  the  light,  for 
concentrating  the  flux  into  a  powerful  beam  or  for  many  of  the 
possibilities  between  these  two  extremes. 

27 


28  THE  LIGHTING  ART 

In  the  consideration  of  the  distribution  of  illumination  and 
brightness  in  the  visual  field  both  the  artistic  and  purely  utili- 
tarian factors  intermingle.  This  aspect  of  distribution  of 
light  is  least  considered  and  developed  yet  it  is  the  most  im- 
portant because  it  involves  the  effect.  The  cause  is  only  of 
incidental  interest  in  lighting  for  the  primary  purpose  is  to 
obtain  a  lighting  result  and  therefore  much  study  and  analysis 
should  be  applied  to  effects.  The  interest  of  the  lighting 
specialist  should  not  cease  on  determining  the  positions  of  the 
outlets  and  on  choosing  the  lighting  equipment  which  will 
provide  a  certain  intensity  of  illumination,  but  these  should  be 
selected  with  the  aim  to  obtain  a  certain  previsualized  effect. 
The  desired  result,  whether  chiefly  artistic  or  predominantly 
utilitarian,  involves  much  more  than  illumination  intensity  on 
a  given  plane.  This  point  has  been  mentioned  in  previous 
chapters  and  will  be  discussed  in  others  for  it  is  one  of  the  most 
vital  though  one  of  the  most  ignored  factors  in  lighting  practice. 

Before  discussing  the  distribution  of  light  as  pertaining  to 
lighting  effects,  a  few  points  will  be  brought  out  regarding  light- 
ing units  which  are  simple  though  often  overlooked.  Simple 
expedients  are  often  the  finishing  touches  which  are  needed  in 
order  to  make  the  lighting  result  completely  satisfactory.  From 
the  standpoint  of  lighting  effect  the  direction  of  the  dominant 
light  is  important  because  of  the  general  direction  of  the 
shadows  which  are  produced.  Shadows  are  usually  essential 
for  good  seeing  and  for  artistic  effect  but  the  character  of  the 
shadows  varies  considerably  depending  upon  three  factors. 
The  direction  of  the  shadows  depends  upon  the  position  of  the 
dominant  light-source.  The  character  of  the  edges  of  the 
shadows,  that  is,  of  the  modulation  in  brightness  from  the 
deepest  shade  to  the  brightness  of  the  surroundings  or  back- 
ground, depends  upon  the  solid-angle  subtended  by  the  light- 
source  at  the  shadow-producing  edge.  The  appearance  of  the 
shadow-edges  is  extremely  important  both  from  the  purely 
utilitarian  and  purely  artistic  viewpoints.  This  may  be 
readily  proved  by  comparing  the  shadows  due  to  a  clear  con- 
centrated filament  lamp  with  those  obtained  after  a  small  dif- 
fusing globe  has  been  placed  over  the  light-source.  The  dif- 


DISTRIBUTION  OF  LIGHT 


29 


ference  is  very  noticeable  even  with  clear  and  frosted  or  opal 
lamps  in  an  ordinary  table  lamp.  Furthermore,  the  difference 
is  not  only  noticeable  but  the  relative  desirabilities  of  the  two 
light-sources  are  usually  easy  to  ascertain.  Consider  the  upper 
edge  of  an  opaque  object  O,  Fig.  i.  The  appearance  of  the 
shadow-edge  on  the  surface  S  will  be  the  same  for  the  light- 
source  of  the  magnitude  of  A  A  as  for  BB.  It  will  be  noted 
that  although  BB  is  larger  than  A  A  it  is  more  distant  and  the 
solid-angle  is  equal  in  the  two  cases. 

Another  point  worthy  of  note  in  this  connection  is  the  effect 
of  the  image  of  the  light-source  reflected  from  glossy  surfaces. 


FIG.  i. — Shadow  cast  by  an  edge  of  an 
opaque  object. 


FIG.  2. — Shadow  cast   by  a  small 
object.    U,  umbra;  P,  penumbra. 


Usually  a  source  of  low  brightness  is  less  annoying  although 
this  is  not  always  true  when  the  light-source  subtends  a  large 
solid-angle  because  it  is  difficult  to  avoid  seeing  a  portion  of  the 
reflected  image.  However,  this  is  largely  dependent  on  the 
character  of  the  surface  and  as  a  consequence  it  is  well  to  avoid 
the  use  of  glossy  surfaces.  There  are  special  operations,  such 
as  the  surfacing  of  metal,  which  depend  upon  specular  reflec- 
tion for  close  inspection  of  the  results;  in  these  cases  a  light- 
source  subtending  a  relatively  small  solid-angle  is  usually 
desirable. 

Shadows  are  also  affected  by  the  amount  of  scattered  light 
received  from  the  surroundings.  If  there  were  no  scattered 
light  the  shadows  would  be  black  except  for  the  penumbra  as 
shown  in  Fig.  2  where  L  is  the  light-source;  0,  the  opaque  ob- 
ject; P,  the  penumbra;  5,  the  receiving  surface;  and  U,  the 
umbra.  The  umbra  receives  no  light  except  from  the  surround- 
ings. The  illumination  of  the  umbra  varies  with  many  con- 
ditions but  measurements  indicate  that  this  is  of  the  order  of 


30  THE  LIGHTING  ART 

magnitude  of  5  to  15  per  cent,  of  the  adjacent  illumination  under 
ordinary  lighting  conditions.  Harshness  or  severity  in  effect 
is  obtained  by  means  of  dark,  sharp  shadows.  It  will  be  noted 
that  the  appearance  of  the  shadow  will  be  altered  on  moving 
S  farther  from  the  object.  In  the  case  of  small  objects  and 
ordinary  light-sources  these  shadows  become  quite  incon- 
spicuous if  cast  on  surfaces  which  are  not  close  to  the  objects. 
A  few  studies  of  shadow-formation  by  means  of  simple 
observation  are  helpful  in  lighting  practice. 

Some  of  these  points  will  be  discussed  in  connection  with 
lighting  units  to  further  emphasize  the  importance  of  these 
details.  The  light  at  a  given  point  in  a  room  may  be  extremely 
diffused  when  received  from  the  ceiling  which  is  illuminated 
by  means  of  a  so-called  indirect  unit.  Although  the  resultant 
diffusion  may  not  be  materially  different,  the  appearance  of  the 
ceiling  will  depend  upon  the  character  of  the  primary  light- 
source  and  upon  other  factors.  The  indirect  unit  is  in  prin- 
ciple, a  shade  and  a  reflector  combined  and  inverted.  If  a 
concentrated  light-source  is  used  the  shadows  of  the  edge  of 
the  bowl  or  of  the  supports  will  appear  sharply  outlined  on 
the  ceiling.  By  frosting  the  lamp  or  by  otherwise  enclosing  it 
in  a  diffusing  medium,  the  effective  light-source  is  made  to 
subtend  a  large  solid-angle  at  the  edge  of  the  bowl  or  at  the 
supports,  owing  to  its  proximity  to  these,  and  the  shadows  are 
no  longer  harsh.  These  objectionable  shadows  may  not  be 
eliminated  entirely  by  this  method  if  only  one  light-source 
per  lighting  unit  be  used  but  those  remaining  will  be  indefinite 
and  often  the  effect  is  more  artistic  than  if  absent  entirely. 
Artistically  there  are  few  places  for  harsh  shadows  in  lighting. 

The  foregoing  also  applies  to  semi-indirect  bowls  and  shades 
and  many  harsh  effects  could  be  eliminated  by  such  simple 
expedients.  Very  often  a  harsh  spot  on  the  wall  adjacent  to 
a  bracket  fixture  may  be  softened  by  replacing  the  clear  lamp 
with  a  frosted  lamp,  by  placing  a  sheet  of  sand-blasted  glass  or 
other  diffusing  medium  over  the  aperture  of  the  shade,  by 
scalloping  or  corrugating  the  edge  of  the  shade  and  by  other 
obvious  methods.  The  shadow-effect  of  a  bare  light-source  is 
rendered  less  harsh  even  by  an  opaque  aluminized  or  enamelled 


DISTRIBUTION  OF  LIGHT  3] 

reflector  because  the  light-source  now  consists  in  reality  of  two 
light-sources,  namely,  the  bare  lamp  and  the  reflecting  surface. 
Often  semi-indirect  bowls  appear  spotted  and  ugly  because  of 
the  improper  mounting  of  the  light-sources  within  them, 
although  in  order  to  present  an  artistic  appearance,  the  bowls 
need  not  present  a  perfectly  uniform  appearance.  Some  of  the 
most  beautiful  appearances  of  such  luminous  bowls  are  due  to 
non-uniform  brightness-distribution  in  which  the  light  and  shade 
is  delicately  blended.  The  artistic  possibilities  of  variety 
extend  to  such  bowls  as  well  as  to  lighting  effects  as  a  whole. 

Various  reflectors  giving  asymmetrical  distributions  of  light 
are  available  for  use  on  brackets  and  behind  cornices  and  these 
make  possible  the  production  of  some  excellent  effects  in 
lighting.  They  perform  the  double  function  of  eliminating  the 
conspicuous  adjacent  bright  spot,  which  is  one  of  the  objec- 
tionable features  of  the  ordinary  unit,  and  of  projecting  the 
light  to  other  parts  of  the  ceiling  and  walls  where  it  may  be 
desired.  Such  units  have  greatly  extended  the  possibilities  of 
lighting  by  means  of  fixtures  supported  on  the  walls.  They  may 
be  placed  on  brackets,  concealed  in  imitation  flower-boxes 
or  behind  decorative  ornaments,  or  hidden  in  recesses  designed 
by  the  architect.  Such  units  of  asymmetrical  distribution  have 
wide  applications  in  many  places  such  as  corridors,  rotundas, 
large  rooms,  and  even  in  the  home. 

Artificial  lighting  systems  are  commonly  divided  into  three 
broad  classes,  namely,  direct,  semi-indirect,  and  indirect  sys- 
tems, although  this  classification  has  no  other  justification 
than  that  of  convenience  because  there  are  no  definite  bound- 
aries between  the  classes  and  much  less  distinction  between 
them  on  the  basis  of  the  lighting  effects  which  are  obtained. 
A  light-source  equipped  with  a  pendant  opaque  reflector  may 
be  called  a  direct-lighting  unit.  If  this  unit  be  inverted  it 
becomes  an  indirect-lighting  unit  because  the  light  reaches  the 
working  area  indirectly  by  reflection  from  the  ceiling,  walls, 
etc.  Between  these  two  extremes  we  have  an  infinite  variety 
of  lighting  units  and  lighting  effects. 

If  the  pendant  opaque  reflector  be  replaced  by  an  opal  or 
prismatic  glass  shade,  the  unit  is  ordinarily  considered  a  direct- 


32 


THE  LIGHTING  ART 


lighting  unit  although  the  lighting  effect  has  been  altered  very 
considerably.  If  this  unit  be  inverted,  we  have  what  may  be 
termed  a  semi-indirect  lighting  unit.  With  the  wide  variation 
in  the  densities  of  glassware  and  in  the  design  of  lighting  units 
employing  diffusely  transmitting  media,  there  is  a  great  variety 
in  lighting  effects  which  may  be  included  in  the  classification 
of  so-called  semi-indirect  lighting.  Considering  the  light 

^100 


H 


0* 


80 


uo 

00 
UJO 


20 
0 


o 
100  V, 

FIG.  3. — Diagrammatic  illustration  of  the  distribution  characteristics  of  lighting 

units. 

density  glass  bowls  the  lighting  effect  may  be  comparable  with 
that  obtained  from  the  pendant  diffusing  glass  ball  though  the 
latter  is  never  classed  as  a  semi-indirect  unit. 

The  simple  diagram  shown  in  Fig.  3  illustrates  all  possible 
combinations  of  direct  and  indirect  (downward  and  upward) 
components  of  light  flux  obtained  from  lighting  units.  For  the 
sake  of  being  definite,  the  downward  component  might  be  con- 
sidered that  portion  of  the  total  output  of  light-flux  which  is 
emitted  into  the  lower  hemisphere,  and  the  upward  component 
that  portion  emitted  into  the  upper  hemisphere.  The  hori- 
zontal plane  HH  may  be  considered  to  pass  through  the 


DISTRIBUTION  OF  LIGHT  33 

center  in  the  lighting  unit  which  must  be  considered  to  be  with- 
out dimension  for  the  sake  of  diagrammatic  illustration. 
Purely  direct  lighting  is  represented  at  a  and  indirect  lighting 
at  /.  Between  these  two  extremes  is  a  vast  variety  of  direct- 
indirect  lighting.  It  appears  that  scientific  lighting  termi- 
nology would  be  simplified  and  rendered  more  definite  if  the 
term  "  semi-indirect "  should  be  replaced  by  the  term  direct- 
indirect.  A  given  unit  could  then  be  specified  in  such  a  manner 
as  direct-indirect,  30-70,  which  would  signify  a  30  per  cent, 
downward  component  and  a  70  per  cent,  upward  component 
and  thus  eliminate  the  confusion  and  indefiniteness  of  the  term 
"semi-indirect." 

Satisfactory  semi-indirect  units  are  usually  found  to  have 
characteristics  in  the  region  between  e  and  /,  Fig.  3,  and  the 
so-called  luminous-bowl  units  possess  characteristics  approach- 
ing close  to  /.  If  the  lighting  units  are  exposed  to  the  normal 
field  of  view  it  has  been  fairly  well  established  that  their 
characteristics  as  to  upward  and  downward  components 
ordinarily  should  lie  between  e  and  /. 

A  more  definite  requirement  in  practice  is  a  quantitative 
limit  of  brightness  because  a  large  diffusing  glass  globe  or  bowl 
of  light-density  glass  would  be  satisfactory  if  the  luminous  out- 
put of  the  light-source  were  sufficiently  small.  If  a  light- 
source  of  high  luminous  output  were  used  in  such  units  the 
brightness  of  the  diffusing  glass  might  exceed  the  satisfactory 
limit.  The  brightness  of  such  units  as  established  by  what  is 
considered  good  practice  at  present  varies  from  0.25  to  i.o 
candle  per  square  inch  or  approximately  from  0.125  to  0.5 
lambert  (125  to  500  millilamberts) .  For  the  more  exacting 
work  where  the  position  of  the  observer  is  definitely  fixed  the 
lower  values  are  preferable.  There  are  many  factors  such  as 
brightness-contrast  and  the  position  of  the  units  which  de- 
termine the  limiting  brightness  so  that  it  is  impossible  to  be 
very  definite  without  discussing  these  factors  at  great  length. 
Specifications  of  brightness  apply  to  the  unit  as  installed  and 
equipped  with  light-sources  whereas  the  direct-indirect  classi- 
fication has  the  advantage  of  definiteness  regarding  the  dis- 
tribution of  light  obtainable  from  the  unit. 


34  THE  LIGHTING  ART 

Such  a  classification  or  specification  of  lighting  units  in  terms 
of  direct  and  indirect  components  appears  to  satisfy  certain 
practical  requirements  of  definite  description  of  the  character- 
istics of  individual  units  but  there  is  still  a  lack  of  definiteness 
in  the  description  of  lighting  installations  in  general,  unless  such 
a  classification  be  applied  to  the  distribution  of  light  as  a  whole. 
Cove-lighting  in  which  the  light-sources  are  concealed  behind  a 
projecting  moulding  or  cornice  would  be  correctly  classified  as 
indirect  lighting  and  there  appears  to  be  no  reason  why  the 
direct-indirect  terminology  could  not  be  applied  to  the  distri- 
bution of  light  by  the  lighting  system  as  a  whole  as  determined 
at  any  point  of  interest.  However,  no  such  classification  can 
be  applied  to  the  lighting  effects  because  these  are  measured  in 
terms  of  brightness-distribution  which  depends  upon  reflection- 
factors  and  therefore  upon  many  elements  such  as  decoration. 

The  foregoing  discussion  has  dealt  with  the  common  artificial 
lighting  systems  from  the  standpoint  of  distribution  of  light; 
however,  the  distribution  of  daylight  in  interiors  is  important 
not  only  by  itself  but  in  connection  with  artificial  lighting. 
There  is  much  of  interest  in  the  study  of  daylight  distribution 
because  it  presents  more  widely  different  effects  than  are  com- 
monly encountered  in  artificial  lighting.  Oddly  enough,  rel- 
atively little  study  has  been  applied  to  daylight  distribution 
compared  with  the  vast  amount  of  measurements  which  have 
been  applied  to  artificial  lighting.  A  need  in  lighting  practice 
is  a  more  general  analytical  study  of  the  distributions  of  illu- 
mination and  of  brightness  on  various  planes  and  at  various 
points  instead  of  confining  the  studies  to  the  so-called  horizontal 
or  other  work -plane.  These  measurements  are  gradually  being 
extended  in  scope  and  it  is  certain  that  they  are  resulting  in 
material  progress  in  the  proper  use  of  light.  Although  quanti- 
tative measurements  are  desirable,  much  is  to  be  gained  by 
qualitative  analyses  of  the  varied  lighting  conditions  about  us. 

In  general,  daylight  indoors  varies  widely  in  distribution 
from  that  obtained  from  any  ordinary  system  of  artificial 
lighting  except  in  the  relatively  rare  cases  where  overhead 
diffusing  skylights  are  used  to  admit  daylight.  Daylight 
usually  enters  interiors  from  vertical  openings  at  the  sides  of  the 


DISTRIBUTION  OF  LIGHT  35 

room  and  inasmuch  as  most  of  the  light  is  directed  through  these 
openings  from  the  sky  or  sun  overhead,  the  illumination  is 
usually  of  the  greatest  intensity  on  the  floor.  In  order  to  simu- 
late the  distribution  of  brightness  outdoors  to  which  the  eye 
has  been  adapted  for  ages,  there  doubtless  arose  the  habit  of 
using  floor-coverings  of  a  dark  shade  and  of  finishing  the  ceil- 
ing and  upper  parts  of  the  walls  in  lighter  shades.  Although  the 
illumination  of  the  ceiling  under  these  daylighting  conditions 
is  usually  of  a  much  lower  intensity  than  that  of  the  floor,  the 
light  which  reaches  it  by  reflection  from  the  floor,  walls,  and 
objects  outdoors,  does  not  suffer  much  absorption  because  of 
the  usual  high  reflection-factors  of  ceilings.  The  effect  is  there- 
fore one  of  high  brightness  for  the  ceiling  and  upper  parts  of 
the  room  and  of  lower  brightness  for  the  floor,  notwithstanding 
the  greater  intensity  of  illumination  on  the  floor.  The  illumina- 
tion distribution  is  sometimes  reversed  when  there  is  snow  on 
the  ground  and  on  other  objects.  In  fact,  it  is  interesting  to 
note  the  tremendous  change  in  the  natural-lighting  effects  in  a 
room  from  season  to  season  and  sometimes  from  hour  to  hour. 
The  foregoing  is  an  excellent  illustration  of  the  difference  be- 
tween illumination  and  brightness;  that  is,  between  cause  and 
effect. 

From  the  viewpoint  of  distribution  of  light  in  an  interior  the 
direct-lighting  system  usually  more  nearly  simulates  daylight 
indoors  in  most  cases  than  does  indirect  lighting.  Brightness 
measurements  and  others  are  very  convincing  in  this  respect. 
But  there  is  generally  an  outstanding  difference  in  the  distribu- 
tion of  artificial  light  and  of  daylight  indoors,  namely,  the 
dominant  direction  of  light.  This  results  in  a  different  direc- 
tion of  shadows,  which  aside  from  the  color-difference  is  perhaps 
by  far  the  greatest  source  of  annoyance.  Many  industrial 
operations  and  many  other  interior  settings  are  adapted  to 
daylighting  and  the  sudden  change  or  conflict  in  the  direction 
of  shadows  when  artificial  light  is  called  upon  to  reinforce  wan- 
ing daylight  causes  such  annoyance  that  this  period  of  the  day 
is  often  unsatisfactory.  There  appears  to  be  an  additional 
annoyance  where  the  difference  in  color  of  the  two  illuminants 
is  conspicuous  as  it  usually  is.  In  such  cases  it  is  often  more 


36  THE  LIGHTING  ART 

advisable  to  make  the  change  completely  from  natural  to  arti- 
ficial light  for  after  a  few  moments  the  eyes  become  readjusted 
and  the  operator  may  shift  himself  or  his  work  to  a  more  satis- 
factory position. 

It  is  not  impossible  or  even  impracticable  in  some  cases  to 
place  the  artificial  lighting  units  so  that  the  dominant  direction 
of  light  is  approximately  the  same  as  that  of  daylight  and  when 
the  illuminant  approximates  daylight  in  color  the  day  wanes  and 
night  falls  without  being  noticed  by  the  busy  person.  The 
greatest  obstacle  against  such  an  asymmetrical  installation 
of  lighting  units  in  cases  where  this  is  practicable,  is  the  prej- 
udice and  habit  of  the  lighting  practitioners.  This  plan  has 
been  used  in  some  cases  for  bench  work,  office  work,  and  in  other 
places  but  these  represent  exceptional  practise.  It  is  certain 
that  this  procedure  will  be  more  general  where  it  is  practicable 
as  the  science  of  lighting  becomes  better  defined  and  more 
exactly  practised.  In  many  cases  where  the  function  of  artifi- 
cial lighting  is  merely  to  aid  daylight  during  its  waning  hour  this 
appears  to  be  wholly  practicable.  Such  cases  are  to  be  found 
in  school  rooms,  offices,  shops,  etc.  However,  there  are  many 
cases  where  artificial  lighting  is  used  for  many  hours  of  the  day 
and  in  these  it  appears  best  to  take  advantage  of  the  superior 
possibilities  of  artificial  lighting  and  to  use  daylight  merely 
secondarily. 

In  simulating  the  distribution  of  daylight  indoors  it  is  possible 
to  illuminate  walls  by  means  of  shaded  units  and  to  obtain  the 
proper  distribution  and  diffusion  of  light  indirectly  by  reflec- 
tion. This  has  even  been  carried  farther  by  placing  in  the 
window  openings,  screens  of  high  reflection-factor  and  illumi- 
nating them  by  means  of  shaded  units.  Such  distributions  of 
light  have  not  been  displeasing  and  have  been  useful  in  over- 
coming the  difficulties  of  the  usual  conflicting  shadows.  In 
large  reading  rooms,  for  example,  where  the  proper  direction  of 
light  is  from  the  left  of^a  person  as  he  sits  reading  or  writing, 
the  furniture  and  artificial  lighting  units  might  well  be  placed 
in  such  a  position  that  the  person  would  be  equally  satisfied  with 
daylight  or  natural  light.  There  are  many  practicable  possi- 
bilities of  such  a  coordination  of  distribution  of  natural  and 


DISTRIBUTION  OF  LIGHT  37 

artificial  light  among  the  vast  variety  of  problems  which  con- 
front the  lighting  specialist  and  the  realization  of  these  possi- 
bilities will  be  found  along  the  highway  of  future  progress  in 
lighting. 

In  this  chapter  an  attempt  has  been  made  to  point  out  the 
general  importance  of  distribution  of  light  in  extracting  from 
among  the  many  possibilities  that  which  best  solves  the  prob- 
lem at  hand.  The  subject  is  as  extensive  as  lighting  itself 
because  the  question  of  distribution  of  light  is  involved  in  every 
problem  regardless  of  magnitude.  It  is  discussed  in  nearly 
every  chapter  of  this  book  but  a  few  specific  points  have  been 
brought  forth  here  in  order  to  emphasize  the  possibilities.  The 
distribution  of  light  as  obtained  from  the  ordinary  systems  of 
lighting  have  their  place  in  lighting  and  the  problem  usually  is 
to  select  that  which  produces  the  desired  effect.  However, 
progress  will  be  marked  by  combinations  of  these  distributions 
and  by  special  ones  devised  for  solving  unusual  problems.  In 
lighting  it  is  the  effect  that  is  sought  and  in  obtaining  this  the 
lighting  unit  is  only  a  necessary  link  for  through  it  and  the  other 
attendant  factors  the  desired  result  is  obtained  by  a  satisfactory 
distribution  of  light  and  color. 


CHAPTER  VI 
LIGHTING  FIXTURES 

The  chief  problem  in  the  design  of  lighting  fixtures  is,  in 
general,  to  combine  beauty  with  utilitarian  or  practical  value. 
The  evolution  of  lighting  fixtures  may  be  definitely  traced  along 
two  lines,  namely,  the  artistic  and  the  scientific  or  practical 
and  in  a  relatively  small  percentage  of  available  fixtures  have 
these  two  lines  merged  harmoniously  into  completely  satis- 
factory results.  Inasmuch  as  the  importance  of  proper-light- 
ing principles  has  become  widely  appreciated  only  within  a 
comparatively  recent  period,  it  is  not  surprising  to  find  that 
the  artistic  viewpoint  was  the  dominant  factor  in  early  fixture- 
design.  In  fact,  the  problems  of  fixture-design  were  early 
placed  in  the  hands  of  the  artist  who  even  today  is  largely  the 
dominant  factor. 

Although  there  are  vast  possibilities  in  utilizing  light  as  a 
decorative  medium  through  lighting  effects  beyond  the  fixture, 
it  is  relatively  rarely  used  with  this  as  a  primary  aim;  there- 
fore it  is  logical  to  conclude  that  the  primary  purpose  of  light- 
ing fixtures  is  to  provide  light  for  utilitarian  or  practical  pur- 
poses. We  thus  arrive  at  a  paradoxical  condition  in  which  the 
scientific  application  of  light  is  found  to  be  chiefly  in  the  hands 
of  the  artist  except  in  purely  utilitarian  lighting  such  as  is 
found  in  the  industries.  Naturally  the  artist's  thought  and 
energy  is  directed  toward  harmony  of  line,  proportions,  and 
other  decorative  features  and  often  through  lack  of  knowledge 
or  appreciation  of  the  value  of  scientific  lighting  principles,  an 
artistic  fixture  is  produced  which  fails  to  perform  its  chief 
function  in  the  best  manner. 

But  may  a  fixture  be  beautiful  if  it  fails  in  its  chief  function 
of  practical  utility?  The  vast  literature  on  the  philosophy 
of  the  beautiful  renders  a  negative  answer  for  beauty  is 
"visible  perfection,  an  imperfect  image  of  the  supreme  perfec- 

38 


LIGHTING  FIXTURES  39 

tion" — a  result  of  harmony  or  the  accord  of  all  the  elements 
such  as  lines,  masses,  colors  and  finally  artistic  and  practical 
functions.  Notwithstanding  the  theoretical  and  idealistic 
conclusions  arrived  at  by  the  philosophers  in  the  realms  of 
beauty  and  value,  it  is  well  to  bear  in  mind  both  the  utility  of 
beauty  and  the  beauty  of  utility  if  for  no  other  reason  than 
for  the  inspiration  to  strive  to  unite  the  practical  and  the  artistic 
aspects  in  lighting  fixtures. 

On  surveying  the  past  in  lighting  it  is  easy  to  imagine  the 
designing  artist  so  absorbed  with  such  elements  as  form,  grace, 
rhythm,  color  and  expression  that  he  neglected  the  principal 
object  of  the  fixture — its  usefulness  as  a  lighting  accessory. 
Similarly  it  is  easy  to  imagine  the  lighting  engineer  so  engrossed 
with  the  scientific  aspects  of  lighting  that  he  neglected  to  culti- 
vate an  appreciation  of  the  artistic  aspect.  It  is  not  a  simple 
task  for  an  individual  to  cultivate  both  viewpoints  to  a  high 
degree  but  it  is  possible.  Dual  experts  of  this  character  are 
rare  but  the  harmonizing  of  science  and  art  in  lighting  fixtures 
can  be  accomplished  by  a  closer  cooperation  between  the  de- 
signing artist  and  the  designing  engineer.  The  past  bears  wit- 
ness in  many  cases  to  the  absence  of  such  combined  efforts. 
Fixture  catalogues  of  today,  although  showing  a  mingling  of 
these  two  viewpoints,  present  a  variety  of  examples  which  pic- 
torially  represent  the  progress  of  science  and  art  toward  each 
other.  Fixture  design  has  evolved  largely  from  the  purely 
artistic  viewpoint  and  in  this  field  lies  the  opportunity  for 
perfecting  the  harmony  of  usefulness  and  beauty  in  lighting. 

It  is  not  always  a  simple  task  to  combine  the  artistic  with 
the  practical;  that  is  to  design  the  skeleton  of  a  scientific 
lighting  fixture  and  then  to  provide  it  with  an  artistic  exterior. 
It  is  satisfying  to  note  that  such  attempts  are  more  frequent 
now  than  in  the  past  and  it  is  easy  to  discern  by  their  output 
those  fixture  manufacturers  who  are  working  toward  this  ideal. 
They  represent  the  successful  and  progressive  manufacturers 
of  today.  An  idea  of  the  amount  of  progress  still  to  be  made 
toward  the  harmony  of  science  and  art  in  lighting  fixtures  may 
be  gained  by  visiting  fixture  display-rooms|with  the  chief  thought 
of  the  foregoing  paragraphs  dominating  the  mind.  If  a  sacri- 


40  THE  LIGHTING  ART 

fice  must  be  made  in  harmonizing  the  practical  and  the  artistic, 
let  it  be,  in  most  cases,  a  sacrifice  of  efficiency  in  its  narrow 
sense.  The  accomplishment  of  the  practical  and  artistic  aims 
simultaneously,  even  at  the  sacrifice  of  some  light,  results  in 
an  efficient  unit  in  the  broadest  sense.  One  handicap  in  the 
design  of  lighting  fixtures  has  gradually  been  lowered  as  the 
efficiency  of  light-production  has  increased  and  today  we  may 
well  afford  luxuries  in  lighting  if  a  few  years  ago  we  could  have 
afforded  the  pure  necessities  for  the  cost  of  light  has  greatly 
diminished.  It  does  not  appear  that  the  general  progress  in 
the  design  of  lighting  fixtures  has  kept  pace  with  the  decrease 
in  the  cost  of  light  if  fixtures  of  the  past  were  justifiable. 

The  lighting  fixture  is  a  means  to  an  end;  its  place  is  always 
between  the  meter  and  the  eye.  For  this  reason  it  is,  doubtless, 
the  most  important  factor  in  the  art  of  illumination  and  may 
be  considered  from  many  viewpoints,  those  of  the  manufac- 
turer, of  the  salesman,  and  of  the  lighting  specialist,  being  of 
special  interest  here.  These  persons  should  know  the  principles 
of  the  art  of  lighting  but  unfortunately  some  manufacturers 
and  many  salesmen  know  relatively  little  of  either  the  scientific 
or  artistic  aspects  of  illumination  and  the  lighting  specialist 
seldom  qualifies  as  a  lighting  artist.  Fixtures  are  too  often 
made  and  sold  as  a  product  quite  independent  of  lighting.  Un- 
fortunately the  consumer  is  usually  quite  indifferent  or  ignorant 
of  the  finer  points  in  lighting  so  that  faulty  fixtures  and  light- 
ing effects  pass  without  protest  and  scanty  stimulation  is  given 
to  progress  in  these  directions  except  by  lighting  practitioners. 
Owing  to  these  various  conditions  it  may  be  stated  with  con- 
fidence that  one  of  the  greatest  deterrents  to  progress  in  proper 
lighting  is  the  faulty  lighting  fixture  which  is  made  in  great 
numbers  and  sold  to  an  unsuspecting  public. 

The  art  of  illumination  involves  physical  optics,  physiological 
visual  phenomena,  and  psychological  effects  of  light,  shade,  and 
color  as  well  as  engineering  principles.  This  brief  sentence 
covers  a  field  which  has  numberless  by-ways  from  the  physics 
of  light-production  to  the  esthetics  of  lighting  effects.  The 
manufacturer  should  sort  out  from  the  vast  amount  of  available 
data  the  specific  knowledge  which  should  be  utilized  in  the 


LIGHTING  FIXTURES  41 

design  of  lighting  fixtures  for  he  cannot  conceive  and  execute 
proper  lighting  fixtures  with  certainty  without  such  knowledge. 
The  array  of  such  products  which  greets  one  in  catalogues  and 
in  display-rooms  is  evidence  of  the  truth  of  the  foregoing  state- 
ment and  the  small  percentage  of  thoroughly  commendable 
fixtures  is  evidence  that  the  statement  should  be  repeated  far 
and  wide.  But  progress  is  being  made  by  a  number  of  manu- 
facturers and  it  is  easy  for  the  lighting  specialist  to  recognize 
the  product  of  those  who  are  combining  knowledge  of  the 
scientific  facts  of  proper  lighting  with  esthetic  taste. 

More  discouraging  than  other  aspects  of  the  fixture  situa- 
tion is  the  salesman's  lack  of  training  in  the  principles  of 
scientific  and  artistic  illumination.  Relatively  rarely  is  the 
consumer  guided  in  his  choice  of  lighting  equipment  by  a  sales- 
man whose  interest  lies  in  selling  proper  lighting  for  he  appar- 
ently does  not  realize  that  the  customer  has  really  come  to 
purchase  lighting  and  not  merely  to  buy  lighting  fixtures.  This 
is  a  condition  in  fixture  stores  which  is  not  universal  but  from 
many  explorations  into  such  stores  the  author  is  emboldened 
by  his  experiences  to  state  that  the  condition  is  quite  general. 
Why  would  it  not  be  a  matter  of  good  business  in  selling 
fixtures  to  give  proper  lighting  as  good  measure  in  the  trans- 
action? Some  progressive  fixture  dealers  are  doing  this  with 
excellent  rest  Its  and  service  in  lighting  should  become  a  slogan 
of  the  fixture  dealer.  Finally,  we  cannot  avoid  the  conclusion 
that  the  average  consumer  is  in  an  unfortunate  position  hemmed 
in  by  indifference  to  and  ignorance  of  proper-lighting  principles. 
He  is  not  a  lighting  expert  nor  could  he  afford  to  ask  the  advice 
of  one  even  if  he  knew  that  it  would  be  to  his  advantage  to  do 
so.  He  must  depend  upon  his  own  judgment,  the  dealer's 
reputation,  or  the  salesman's  recommendations.  If  neither  he 
nor  the  salesman  is  qualified  to  choose  a  proper  lighting  fixture 
it  is  left  to  chance  and  owing  to  the  relatively  low  percentage 
of  eminently  satisfactory  fixtures  in  an  average  display,  his 
chance  of  obtaining  a  suitable  fixture  is  small.  He  will  be 
easily  influenced  by  the  salesman  so  that  progress  in  good  light- 
ing must  depend  largely  upon  the  salesman's  ability  as  a  light- 
ing specialist.  Experience  indicates  that  many  salesmen 


42  THE  LIGHTING  ART 

are  more  concerned  with  the  popularity  of  a  certain  design  than 
with  meeting  the  consumer's  individual  requirements,  with  the 
result  that  there  is  a  vast  number  of  fixtures  in  use  today  which 
should  never  have  been  sold  or  even  made. 

Viewed  from  the  broad  aspect  of  the  art  of  illumination  the 
problem  of  getting  proper  lighting  fixtures  made,  sold  and  prop- 
erly installed  is  an  overwhelming  one  at  the  present  time  yet 
it  must  be  solved  before  general  progress  in  scientific  and  artis- 
tic lighting  will  be  made.  There  are  three  points  of  attack 
which  in  the  order  of  their  choice,  are  perhaps  manufacturing, 
selling,  installing.  More  knowledge  of  lighting  is  required  in 
the  conduct  of  each  of  these  activities  and  if  they  are  well  done 
the  public  will  eventually  become  familiar  with  the  usefulness 
and  pleasure  inherent  in  good  lighting. 

It  is  not  a  primary  aim  in  this  chapter  to  discuss  the  many  de- 
tails of  good  and  bad  lighting  fixtures  for  the  reason  that  such  a 
discussion  would  be  very  extensive  and  would  lead  far  into  the 
incompletely  explored  regions  such  as  the  conservation  of 
vision,  visual  efficiency,  and  esthetic  principles.  Many  aspects 
of  these  fields  have  been  widely  discussed  in  lighting  literature 
so  that  the  progressive  manufacturer,  salesman,  architect,  or 
illuminating  engineer  may  readily  assimilate  from  these  the 
knowledge  which  he  requires.  An  aim  of  all  concerned  with 
lighting  fixtures  should  be  to  safeguard  vision  and  to  add  to  the 
efficiency  and  pleasure  of  mankind  by  means  of  proper  lighting. 

From  the  practical  standpoint  the  fixture  should  shield  the 
primary  light-source  from  ordinary  view  and  excessive  bright- 
nesses of  transmitting  and  reflecting  media  should  be  avoided. 
Contrast  plays  an  important  role  in  visual  comfort  and  the 
maximum  permissible  brightness  depends  upon  the  brightness 
of  the  surroundings.  A  bare  incandescent  lamp  may  be  viewed 
against  a  bright  sky  without  serious  discomfort  but  when  viewed 
against  dark  surroundings  or  even  against  the  ordinary  back- 
ground in  an  interior  it  will  be  glaring.  This  is  an  example  of 
the  importance  of  contrast  in  lighting.  In  the  so-called  semi- 
indirect  systems,  more  definitely  described  as  direct-indirect 
systems,  the  glassware  ordinarily  used  is  often  not  dense  enough. 
Of  course  the  satisfactoriness  of  a  given  diffusing  glass  bowl 


LIGHTING  FIXTURES  43 

depends  upon  the  positions  and  luminous  output  of  the  light- 
sources  inside  the  bowl  but  in  general  the  light-density  diffusing 
glasses,  as  commonly  used,  are  too  bright  for  comfort  unless 
hung  quite  high.  The  same  is  true  of  diffusing  glass  shades. 
The  permissible  maximum  brightnesses  of  lighting  equipment 
are  not  definitely  established  and  depend  upon  so  many  factors 
such  as  the  brightness  of  backgrounds  and  the  hanging-height 
that  it  appears  inadvisable  to  attempt  to  present  quantitative 
data,  although  a  safe  maximum  limit  for  ordinary  conditions 
will  perhaps  be  found  to  lie  between  o.i  and  0.5  lamberts.  For 
the  sake  of  comparison  the  average  sky-brightness  may  be  con- 
sidered to  be  about  i  lambert.  General  experience  and  obser- 
vation must  be  depended  upon  at  present  for  conclusions  re- 
garding these  brightness  factors  but  the  tendency  should  be 
generally  toward  lower  maximum  brightnesses  and  contrasts 
than  are  commonly  encountered. 


abed 
FIG.  4. — Illustrating  simple  though  important  details  in  lighting. 

Throughout  lighting  practice  the  correction  of  apparently 
minor  details,  by  means  of  simple  alterations,  works  wonders 
and  this  applies  with  equal  force  to  lighting  fixtures.  For  ex- 
ample, a  shower  with  small  pendant  glass  shades  may  be  un- 
satisfactory if  hung  too  high  because  the  bare  lamps  may  be 
visible.  If  the  glassware  is  sufficiently  dense  no  other  altera- 
tion may  be  necessary  than  merely  lengthening  the  supporting 
chains  or  rods.  It  may  be  that  the  shades  are  not  deep  enough 
or  that  the  lamp  projects  too  far  downward  so  that  the  light- 
source  is  visible.  By  using  a  shorter  lamp,  by  bowl-frosting 
the  lamp  if  it  is  of  the  electric  incandescent  type,  or  by  provid- 
ing shades  of  a  different  shape  with  a  smaller  aperture,  the 
fixture  may  be  made  satisfactory.  Some  of  these  points  are 
illustrated  in  a  simple  manner  in  Fig.  4  where  under  certain  con- 
ditions a  may  be  unsatisfactory  and  b  satisfactory  owing  to  a 


44  THE  LIGHTING  ART 

slight  alteration  in  the  shape  of  the  shade.  By  using  smaller 
lamps  as  in  c  or  a  deeper  shade,  condition  a  may  be  improved. 
By  bowl-frosting  the  lamp  as  in  d  an  improvement  over  b  may 
be  gained  in  some  cases.  Such  simple  details  in  lighting  are 
often  very  important. 

The  artistic  scheme  of  certain  types  of  fixtures  appears  to 
demand  the  use  of  unshaded  frosted  lamps,  but  unless  these  are 
hung  high  in  the  ordinary  interior  and  the  surroundings  are 
fairly  bright  the  contrast  is  usually  too  great  for  visual  comfort. 
Often  a  simple  artistic  shade  may  be  easily  supplied  without 
sacrificing  the  congruity  of  the  whole  and  thus  make  the  fixture 
satisfactory.  Such  frosted  lamps  on  brackets  against  a  dark 
wall  often  are  sources  of  glare  from  which  there  is  no  escape. 
Many  installations  of  this  character  are  in  existence,  forming 
delightful  harmonies  with  the  decorative  scheme  when  unlighted, 
which  testifies  to  the  artistic  ability  of  the  architect  but  also  to 
his  failure  to  visualize  the  lighting  effect.  The  same  may  be 
said  of  some  of  the  gorgeous  glittering  effects  of  bespangled 
fixtures  befitting  the  Renaissance  period.  These  are  delight- 
fully congruous  with  the  surroundings  when  unlighted  and 
doubtless  were  satisfactory  in  the  period  in  which  they  evolved 
when  candles  of  low  intrinsic  brightness  were  used,  but  with 
modern  light-sources  of  hundreds  of  times  greater  brightness 
such  units  are  very  annoying.  Chandeliers  are  often  beautiful 
fixtures  but  the  excessive  brightnesses  of  modern  light-sources 
usually  make  it  necessary  to  use  diffusing  shades  which  inter- 
rupts the  artist's  decorative  scheme.  As  science  progresses 
even  art  must  alter  its  traditions  in  order  to  meet  the  first 
requirement  of  lighting,  namely,  safe  and  comfortable  vision. 

In  fact,  the  high  brightnesses  of  modern  light-sources  have 
made  it  imperative  to  curb  the  traditional  freedom  of  the  artist. 
As  long  as  only  light-sources  of  low  brightness  such  as  the  candle 
flame  existed,  vision  was  not  endangered  or  often  annoyed  and 
the  only  criticism  that  could  be  applied  was  one  of  inefficiency 
in  the  use  of  light.  This  latter  criticism  has  dwindled  in  im- 
portance with  the  modern  high  efficiency  of  light-production 
but  the  other  criticisms  become  exceedingly  important  because 
they  aim  at  the  conservation  of  a  human  resource  which  is 


LIGHTING  FIXTURES  45 

irreplaceable  and  incomparable  in  value  with  cost  of  lighting. 
As  much  as  we  would  like  to  preserve  the  art  of  the  past  in 
lighting  fixtures,  scientific  progress  in  light-production  makes 
it  necessary  to  abandon  some  of  it  or  to  modify  it  to  meet  the 
more  urgent  demands  of  safe  and  comfortable  vision. 

In  many  interiors  and  even  in  some  modern  fixture  displays, 
designs  are  found  which  are  relics  of  the  early  days  of  gas  flames 
and  carbon  incandescent  lamps.  These  fixtures,  consisting 
of  curved  arms  supporting  small  glass  shades  oriented  in 
various  directions  which  confront  the  observer  from  every 
viewpoint,  did  not  seriously  offend  vision  when  used  with  the 
light-sources  for  which  they  were  designed.  Though  of  doubt- 
ful artistic  value  most  of  these  are  now  doomed  to  the  discard 
on  the  basis  of  conserving  vision  because  they  are  quite  unsatis- 
factory with  modern  light-sources  of  high  brightness. 

One  of  the  most  important  viewpoints  in  connection  with 
lighting  fixtures  is  that  of  the  lighting  effect  desired  or  obtained 
from  them.  There  are  numberless  designs  available  which  give 
a  variety  of  effects  which  may  be  included  under  the  classifica- 
tion of  direct-indirect.  In  the  choice  of  a  fixture  two  viewpoints 
are  important  from  the  standpoint  of  lighting.  The  first 
usually  should  be  that  of  the  lighting  effect  obtained  with  the 
fixture  and  the  second  that  of  the  design,  appearance,  and 
various  practical  aspects  of  the  fixture  itself.  A  new  scientific 
design  may  appear  on  the  market  and  just  claims  are  made  as 
to  its  novelty,  appearance,  and  various  practical  features. 
But  claims  may  also  be  made  regarding  the  lighting  effect  when 
as  a  matter  of  fact  this  may  not  differ  materially  from  that  ob- 
tained by  simple,  commonplace  units  that  have  been  in  use  for 
years.  This  may  be  illustrated  in  Fig.  5  where  the  glass 
elements  are  represented  by  dotted  lines,  opaque  elements  by 
full  lines,  and  light-sources  by  crosses.  By  various  combina- 
•  tions  of  clear,  diffusing,  and  prismatic  glass  the  five  lighting 
units  may  be  made  to  give  practically  the  same  lighting  effects, 
especially  if  the  installation  involves  at  least  several  units.  It 
is  fortunate  that  such  a  variety  of  units  are  available  for  a 
certain  lighting  effect  because  it  extends  the  possibilities  of 


46  THE  LIGHTING  ART 

lighting  by  not  limiting  too  narrowly  the  artistic  designs  and 
practical  features  of  fixtures. 

To  further  illustrate  the  point  let  us  take  the  two-circuit 
fixture  in  which  the  desirable  element  of  variety  in  lighting  is 
inherent.  This  is  diagrammatically  illustrated  in  Fig.  6.  By 


/    \     /  \ 

/  \  /  \  A  A  i  i  i 
L A  (.  )  /  A  )  /  *  \  A  A  A 

V  x   •'     W    V  ..-'    '-- s 

^- — ''' 

abed  e 

FIG.  5. — Units   of   different    appearances   which   may   distribute   light    quite 

similarly. 

means  of  various  kinds  of  glass  the  lighting  effects  in  these  cases 
may  be  made  closely  alike  yet  with  variety  in  design.  Three 
distributions  of  light  are  obtainable  in  each  case,  one  from 
each  circuit  separately  and  a  combined  distribution.  From 


a  t>  c  d 

FIG.  6. — Units  providing  a  degree  of  variety  in  distribution  of  light. 

the  symmetry  of  the  light-sources  the  different  circuits  are 
readily  discerned.  These  are  only  a  few  of  the  different  units 
which  may  be  so  designed  and  equipped  with  glassware  as 
to  give  approximately  the  same  lighting  effects.  The  number 
is  limited  only  by  the  mechanical  and  artistic  possibilities. 

It  has  been  the  aim  of  this  discussion  to  indicate  the  important 
place  of  fixtures  in  the  progress  of  lighting  practice.  As  a 
means  to  an  end  they  are  as  important  as  light-sources  and 
should  be  made,  sold,  and  installed  by  those  possessing  a 


LIGHTING  FIXTURES  47 

knowledge  of  the  scientific  and  artistic  principles  of  lighting 
which  are  involved.  A  conspicuous  criticism  which  has  ap- 
peared in  this  discussion  is  that  the  lighting  fixture  is  too  often 
considered  as  being  independent  of  the  chief  aim  of  lighting 
which  is  to  realize  a  desired  effect.  Lighting  fixtures  are  to  be 
looked  at  but  primarily  their  function  is  to  distribute  light; 
therefore  their  artistic  design  should  perform  the  function  of  an 
artistic  drapery  upon  the  scientific  design  which  is  created 
or  chosen  for  the  purpose  of  obtaining  a  desired  distribution  of 
light. 


CHAPTER  VII 
LIGHT  AND  COLOR 

Already  stated  there  are  many  advantages  in  the  study  and 
application  of  lighting  in  its  broadest  sense,  in  separating  the 
analysis  or  problem  into  two  parts  which  deal  respectively, 
with  distribution  and  with  quality  of  light.  In  considering  the 
former  there  is  no  need  for  analyzing  light  itself,  but  in  order 
to  apply  the  scientific  and  artistic  possibilities  of  color  we  must 
delve  deeper  into  light  and  study  the  spectrum,  the  physics  of 
color-mixture,  the  psycho-physiology  of  color-vision  and  the 
psychology  of  color.  Various  chapters  deal  with  these  aspects, 
but  before  the  lighting  specialist  is  able  to  utilize  the  scientific 
possibilities  and  the  charm  of  color  to  their  fullest  extent,  he 
must  be  intimately  acquainted  with  light  itself. 

The  word  "light"  is  indefinite  in  meaning  because  it  is  used 
to  indicate  energy  as  well  as  luminosity  or  light-sensation,  and  in 
this  book  both  of  these  meanings  are  employed  for  the  sake  of 
convenience.  The  light  from  a  tungsten  incandescent  lamp 
appears  to  the  eye  to  be  yellowish- white  in  color;  that  is,  a  tint 
of  yellow.  However,  the  prism  or  diffraction  grating  shows 
it  is  not  homogeneous  but  consists  of  many  colors.  The  light 
from  the  noon-day  sun  on  a  clear  day  is  commonly  considered 
to  be  white,  or  nearly  so,  but  when  a  pencil  of  this  white  light 
is  passed  through  a  glass  prism,  a  spectrum  of  many  hues  from 
violet  to  red  is  seen.  The  number  of  distinctly  different  hues 
which  are  visible  in  a  continuous  spectrum  depends  upon  the 
refinement  of  the  method  of  observation  but  may  be  considered 
to  be  approximately  one  hundred  for  the  sake  of  simplicity. 
The  most  conspicuous  regions  of  the  spectrum  in  their  order  of 
spectral  sequence  are  violet,  blue,  green ,  yellow,  orange,  and 
red. 

A  splendid  analogy  to  the  emission  of  radiant  energy  and  to 
the  perception  of  light  is  that  of  wireless  telegraphy  where  we 

48 


LIGHT  AND  COLOR  49 

have  the  sending  source,  the  receiving  station,  and  the  electro- 
magnetic waves  which  carry  the  message.  Analogous  to  these 
we  have  the  light-source  which  emits  electromagnetic  or  radiant 
energy  of  many  wave-lengths  in  the  case  of  a  high-temperature 
source  such  as  the  sun,  a  gas  mantle,  an  incandescent  filament 
or  a  carbon  arc.  The  retina  of  the  eye  is  the  receiving  station 
tuned  to  respond  to  a  certain  narrow  range  of  wave-lengths 
which  are  included  in  what  is  termed  the  "visible  spectrum." 
But  each  train  of  waves  of  a  given  wave-length  produces  a 
sensation  of  a  certain  hue  distinct  from  that  caused  by  a  train 
of  waves  of  any  other  wave-length.  The  electromagnetic 
or  radiant  energy  of  the  shortest  wave-lengths  to  which  the 
visual  process  responds  produces  the  sensation  of  violet  and  the 
longest,  the  sensation  of  deep  red.  Owing  to  their  minuteness 
these  wave-lengths  are  measured  in  terms  of  very  small  units, 
one  of  the  commonest  being  the  micron  which  is  one-millionth 
of  a  meter  or  one-thousandth  of  a  millimeter  in  length  and 
is  designated  by  the  Greek  letter,  /*•  The  symbol  MM  is  one- 
thousandth  M  or  one-millionth  of  a  millimeter. 

It  is  unnecessary  to  go  far  into  the  details  of  the  production 
of  the  spectrum  for  these  lie  in  the  realm  of  color  not  of  primary 
interest  here.  When  a  pencil  of  sunlight  is  passed  through  a 
glass  prism,  energy  of  short  wave-lengths  is  deviated  more  by 
refraction  than  energy  of  longer  wave-lengths,  with  the  conse- 
quence that  the  pencil  is  spread  out  like  a  fan  on  emerging  from 
the  prism,  and  the  various  trains  of  waves  of  different  wave- 
lengths are  thus  separated  and  the  spectrum  results.  Nature 
presents  the  spectrum  of  sunlight  in  the  rainbow,  the  various 
rays  of  different  wave-lengths  being  separated  in  a  similar 
manner  by  the  raindrops.  When  viewing  such  a  spectrum 
each  portion  of  the  retina  covered  by  the  retinal  image  of 
the  spectrum  is  stimulated  by  a  single  train  of  waves  each  ho- 
mogeneous as  to  wave-length,  with  the  result  that  the  different 
spectral  hues  are  seen.  If  a  white  card  be  illuminated  by  the 
integral  light  from  the  sun,  each  portion  of  the  retinal  image 
is  being  stimulated  simultaneously  by  visible  energy  of  all 
wave-lengths  and,  though  all  color-sensations  are  probably 
aroused,  the  integral  result  is  a  sensation  of  white.  Thus 


50  THE  LIGHTING  ART 

the  eye  alone  cannot  analyze  light  spectrally  and  the  visual 
process  is  said  to  be  synthetic  with  respect  to  color.  It  may 
be  well  to  note  at  this  point  that,  in  general,  the  eye  alone  should 
not  be  trusted  to  estimate  the  spectral  character  or  quality  of 
illuminants  or  of  colored  media  by  mere  visual  inspection, 
for  the  color-sensation  in  the  eye  is  always  the  integral  result 
of  all  the  individual  color-sensations  which  may  be  due  to  the 
radiant  energy  of  the  various  wave-lengths  present  in  the 
illuminant  or  reflected  or  transmitted  by  colored  media. 

In  the  study  of  illuminants  and  of  colored  media  the  spec- 
tral analyses  are  generally  recorded  in  terms  of  energy  of  various 
wave-lengths.  However,  the  eye  is  not  equally  sensitive  to 
energy  of  various  wave-lengths.  It  is  most  sensitive  for  energy 
producing  the  sensation  of  yellow-green,  which  lies  in  the  mid- 
dle of  the  visible  spectrum,  and  the  sensitivity  decreases  rapidly 
toward  the  ends  of  the  spectrum.  The  visibility  of  radiant 
energy  of  various  wave-lengths  has  long  been  a  subject  of  re- 
search, yet  even  today  these  visibilities  have  not  been  estab- 
lished precisely;  that  is,  the  results  of  different  investigators 
do  not  exactly  agree. 

It  is  out  of  the  question  to  discuss  the  many  aspects  of  the 
science  of  color  in  a  book  devoted  to  lighting.  These  have  been 
treated  elsewhere1  but  a  glimpse  of  a  few  of  the  chief  aspects  will 
be  attempted  here  in  order  that  following  chapters  may  be 
more  easily  understood. 

From  the  viewpoint  of  color  in  lighting  the  spectral  charac- 
teristics of  illuminants  are  of  primary  interest.  Light-sources 
which  radiate  energy  owing  to  their  high  temperature  are  found 
to  exhibit  continuous  spectra;  that  is,  if  the  temperature  is 
sufficiently  high,  radiation  of  all  visible  wave-lengths  is  emitted. 
Until  a  color-temperature  nearly  as  high  as  that  of  the  sun  is 
reached,  energy  of  the  longer  wave-lengths  predominates  and 
as  the  temperature  of  the  sun  is  not  reached  in  any  light- 
sources  available  at  present,  all  illuminants  of  this  character  are 
yellowish  in  color.  For  example,  if  a  rheostat  be  placed  in 
series  with  a  tungsten  lamp  it  will  be  found  that  current  may  be 
passed  through  the  filament  without  heating  it  sufficiently  to 

1M.  LUCKIESH:  "Color  and  Its  Applications,"  D.  Van  Nostrand  Co.,  1915. 


LIGHT  AND  COLOR  51 

make  it  glow.  If  the  experiment  is  performed  in  a  dark  room, 
it  will  be  found  on  increasing  the  current  sufficiently  that  the 
filament  will  begin  to  glow  a  deep  red  in  color.  At  this  point 
the  radiation  emitted  consists  almost  entirely  of  red  rays.  As 
the  temperature  is  increased  the  filament  becomes  brighter  and 
the  color  changes  to  orange  indicating  that  energy  of  shorter 
wave-lengths  is  being  emitted  although  the  red  rays  still  pre- 
dominate. The  integral  sensation  caused  by  the  simultaneous 
stimulations  of  the  retina  by  the  radiant  energy  of  various  wave- 
lengths is  an  orange  tint.  The  filament  may  be  increased  in 
temperature  until  it  melts,  yet  at  no  time  does  the  integral 
color  of  the  light  appear  white  if  compared  with  noon  sunlight 
because  the  melting  point  of  the  tungsten  is  far  below  the  tem- 
perature necessary  to  produce  white  light.  The  yellowish  color 
indicates  that  the  rays  of  longer  wave-length  predominate  at 
all  temperatures  at  which  the  tungsten  may  be  operated.  This 
is  also  true  of  the  crater  of  the  carbon  arc  and  of  other  artificial 
illuminants  emitting  light  by  virtue  of  their  high  temperature 
as  this  is  ordinarily  considered.  The  progress  in  light-produc- 
tion by  heating  substances  to  a  high  temperature  has  been 
toward  higher  temperatures  because  of  the  higher  luminous 
efficiencies  obtainable  and  the  progress  in  color  has  been  with 
the  filament  lamps  for  example,  from  the  yellow  light  of  the 
carbon  lamp  to  the  yellowish- white  of  the  tungsten  lamps. 

Incandescent  gases  emit  discontinuous  spectra  usually  in  the 
form  of  narrow  lines  or  bands  in  various  regions  of  the  spectrum. 
These  spectra  are  always  characteristic  of  the  elements  or  gase- 
ous compounds  and  this  fact  has  formed  the  basis  for  spectrum 
analysis  so  valuable  in  chemistry.  The  flames  of  arcs  and  the 
mercury- vapor  lamps  emit  line  spectra;  the  visible  spectrum  of 
the  latter  consisting  chiefly  of  lines  of  wave-lengths  0.408/4, 
0.436/4,  0.546/4,  and  0.578/4  being  respectively  violet,  blue,  yel- 
low-green, and  yellow  in  color.  The  different  elements  with 
which  carbons  are  impregnated  are  chiefly  responsible  for  the 
various  colors  obtained  from  the  flaming  arcs.  The  Moore 
nitrogen  tube  emits  light  of  a  pinkish  color  which  is  the  inte- 
gral color  of  the  combined  color-sensations  due  to  the  line- 
spectrum  of  nitrogen.  The  carbon-dioxide  vacuum  tube  emits 


52 


THE  LIGHTING  ART 


a  line-spectrum  containing  a  great  many  lines  and  the  integral 
color  as  well  as  the  spectrum  itself  closely  approximates  an 
average  daylight  consisting  of  a  mixture  of  direct  sunlight  and 
skylight.  Many  different  colored  lights  may  be  obtained  by 


260 
240 
220 
200 
160 
160 
140 
120 
100 
60 
60 
40 
20 


A- Candle  Flame 

B-  Tungs-ren  (Vacuum),  7.9  Lumens  per  Wcrrr 

C-      »  (Gas)  ,22      »         »       »» 

D-Welsbach    Mantle 

E-Sunligtrr 

F-Skylighi- 

6 -Mercury  Arc  (Lines) 


0.40/* 
Violet 


0.45  0.50  0.55  0.60  0.65 

Blue  Green  Yellow  Orange  Red 

WAVE-LENGTH    AND    HUE 
FIG.  7. — Distribution  of  radiant  energy  in  various  spectra. 


0.70 


electrically  exciting  various  gases  and  beautiful  effects  are  thus 
possible  although  such  light-sources  are  not  very  practicable  at 
the  present  time.  It  is  possible  that  the  future  may  witness 
developments  along  this  line  and  the  production  of  a  wider 
variety  of  colored  lights  directly  from  the  light-source. 

In  Fig.  7  are  shown  the  spectral  energy-distributions  of  a 


LIGHT  AND  COLOR  53 

/ 

number  of  common  illuminants  plotted,  for  the  sake  of  com- 
parison, to  equality  near  the  middle  of  the  spectrum.  Vari- 
ous points  in  the  foregoing  discussions  are  exemplified  in  the 
figure.  The  short  vertical  lines  indicate  the  spectrum  of  the 
mercury  arc.  In  general,  the  predominance  of  radiant  energy 
of  the  longer  wave-lengths  or  yellow,  orange,  and  red  rays  in 
artificial  illuminants  is  to  be  noted. 

The  next  important  aspect  of  color  in  lighting  is  the  effect  of 
the  illuminants  upon  the  appearance  of  a  colored  object.  It 
may  be  taken  as  a  fundamental  axiom  that  a  colored  object 
will  not  appear  the  same,  in  general,  under  two  illuminants  dif- 
fering in  spectral  character.  A  red  fabric  appears  red  under 
daylight  or  under  a  tungsten  lamp  because  it  has  the  ability  to 
reflect  the  red  rays  and  to  absorb  all  or  nearly  all  of  the  other 
colored  rays.  But  the  color  of  the  red  fabric  depends  upon 
the  illuminant  because,  for  example,  it  will  appear  black  or  a 
brownish-black  under  an  ordinary  mercury  arc.  In  a  preced- 
ing paragraph  the  wave-lengths  of  the  important  lines  in  the 
spectrum  of  a  mercury  arc  are  given  and  it  is  seen  that  no  red 
lines  appear.  If  the  illuminant  emits  no  red  rays  and  the  red 
fabric  reflects  no  other  rays,  it  is  obvious  that  it  will  appear 
black  because  the  luminosity  of  a  reflecting  medium  is  due  to 
the  visible  radiant  energy  which  is  reflected  by  it  toward  the 
eye.  The  energy  which  is  absorbed  disappears  as  radiation 
and  is  generally  converted  into  heat. 

There  are  some  characteristics  of  colored  media  which  should 
be  of  interest  to  the  lighting  specialist.  Some  dyes  and  other 
substances  have  the  property  of  fluorescence  or  phosphor- 
escence, the  former  being  a  momentary  phenomenon  as  distin- 
guished from  the  persistence  of  the  latter.  Usually  these 
phenomena  are  excited  by  ultra-violet  energy  and  that  of  the 
short  visible  wave-lengths  but  the  light  which  is  emitted  gen- 
erally bears  no  resemblance  in  color  to  that  of  the  exciting  light. 
Such  a  fluorescent  dye  as  rhodamine  appears  red  when  illu- 
minated by  the  radiation  from  a  mercury  arc  because  it  absorbs 
energy  of  short  wave-lengths  and  emits  energy  of  long  wave- 
lengths. This  phenomenon  has  been  taken  advantage  of  by 
Dr.  Hewitt  and  applied  to  the  mercury-arc  unit  in  the  form  of 


54  THE  LIGHTING  ART 

a  dyed  reflector  thus  adding  red  rays  and  thereby  reducing  the 
distortion  of  colors  under  the  light  from  the  mercury  arc. 

Although  no  certain  estimate  of  the  spectrum  of  a  color  can 
be  made  by  the  eye  alone,  it  may  be  helpful  to  indicate  in  a 
general  manner  the  spectral  colors  which  will  be  found  in  the 
light  reflected  or  transmitted  by  ordinary  colored  media  such 
as  pigments,  dyes,  and  glasses  most  commonly  encountered.1 
These  are  indicated  below  by  means  of  six  spectral  hues,  it 
being  understood  that  the  hues  lying  between  these  in  the 
spectrum  are  also  present  and  that  the  analyses  are  only 
roughly  approximate. 

APPROXIMATE  SPECTRAL  CHARACTERS  OF  A  FEW  COLORS  AS  COMMONLY 

ENCOUNTERED 

Violet — violet,  blue,  some  green,  and  often  deep  red. 
Blue — violet,  blue,  green,  and  often  deep  red. 
Green — blue,  green,  and  yellow. 
Yellow — green,  yellow,  orange,  and  red. 
Orange — yellow,  orange,  and  red. 
Red — orange,  red,  and  sometimes  deep  violet. 
Purple — red,  violet,  and  blue. 

Colored  media  which  are  ordinarily  available  rarely  exhibit 
colors  of  high  purity  or  saturation,  the  dyes  and  glasses  usually 
being  more  satisfactory  in  this  respect  than  pigments. 

At  this  point  it  may  be  helpful  to  outline  roughly  the  hues  of 
the  spectrum  in  relation  to  wave-length,  it  being  understood 
that  these  divisions  are  only  roughly  approximate. 

THE  APPROXIMATE  DISTRIBUTION  or  COLOR  IN  THE  SPECTRUM 

Violet limit  to  0.43;* 

Blue 0.43/4  to  0.47/4 

Blue-green 0.47/1  to  0.50/4 

Green 0.50;*  to  0.53/11 

Yellow-green Q-53M  to  0.56/4 

Yellow 0.56/4  to  0.59/4 

Orange O-59M  to  0.62/4 

Red 0.62/4  to  limit 

The  limits  of  the  visible  spectrum  vary  with  many  conditions 
and  with  different  persons.  For  most  practical  purposes  the 

1  The  spectral  characteristics  of  many  pigments,  dyes,  and  glasses  will  be  found 
in  a  paper  by  the  author  on  "The  Physical  Basis  of  Color-Technology,"  Jour. 
Frank.  Inst.,  vol.  184,  p.  73,  227,  1917. 


LIGHT  AND  COLOR  55 

limits  are  o.4/x  to  0.7/4  but  it  is  usually  possible  under  intense 
illumination  to  experience  the  sensation  of  light  from  radiant 
energy  of  any  wave-length  between  0.39^  and  0.78^. 

Although  the  light-sources  available  at  present  differ  con- 
siderably in  color  they  do  not  present  a  variety  of  colors  pure 
enough  for  producing  many  color  effects  either  artistic  or  spec- 
tacular except  in  special  cases  where  they  are  peculiarly 
adaptable.  Furthermore,  these  colors  are  usually  quite  acci- 
dental as  determined  by  the  exigencies  of  industrial  practice 
or  economy,  and  do  not  provide  tints  which  may  be  har- 
moniously blended  for  artistic  purposes  in  ordinary  interiors. 
They  have  been  utilized  in  special  cases  with  excellent  results, 
for  example,  by  Mr.  Basse tt  Jones  at  the  Allegheny  County 
Soldiers'  Memorial  and  by  Mr.  W.  D'A.  Ryan  at  the  Panama- 
Pacific  Exposition.  But  for  most  requirements  it  is  neces- 
sary to  modify  an  illuminant  by  means  of  colored  screens  in 
order  to  obtain  the  desired  effects.  In  such  cases  a  knowledge 
of  the  spectral  characteristics  of  colored  media  is  applied  in 
making  a  colored  lacquer,  colored  glass  or  other  suitable  filter. 

It  is  comparatively  simple  to  produce  the  required  color  if 
permanency  is  not  a  factor.  Where  this  is  important  and  the 
correction  is  one  such  as  is  required  in  producing  artificial  day- 
light, the  problem  must  be  attacked  from  the  scientific  side  and 
the  spectral  analyses  must  be  made  with  apparatus  which  is 
analytical.  In  many  cases  where  merely  the  subjective  color 
is  of  importance  the  eye  alone  suffices  and  the  proper  tint  may 
be  readily  obtained  by  a  knowledge  of  color-mixture  and  an 
acquaintance  with  colored  media. 

By  the  use  of  colored  filters  two  illuminants  may  be  obtained 
which  appear  exactly  alike  to  the  eye  in  integral  color  though 
spectrally  they  may  be  very  different.  For  example,  two  illumi- 
nants may  appear  white  though  the  spectrum  of  one  may  differ 
very  much  from  that  of  white  daylight;  in  fact,  the  light  from 
the  quartz  mercury  arc  appears  nearly  white  but  its  spectrum 
consists  of  only  a  few  lines  making  it  quite  unfit  for  general 
color  work.  In  a  similar  manner  two  yellows  may  appear 
exactly  alike  to  the  eye  yet  one  may  not  contain  any  spectral 
yellow  at  all  because  green  and  red  light  when  properly  mixed 
will  produce  a  yellow. 


56  THE  LIGHTING  ART 

It  has  been  indicated  in  a  previous  paragraph  that  the  color 
of  an  object  depends  upon  the  spectral  character  of  the  illumi- 
nant.  That  this  is  true  may  be  readily  proved  by  viewing  any 
colored  object  alternately  under  two  different  illuminants. 
Those  illuminants  which  have  discontinuous  spectra  distort 
colors  in  general  very  much  more  than  those  having  continuous 
spectra.  The  variation  in  the  appearance  of  a  colored  object 
under  different  illuminants  is  due  largely  to  the  impurity  or 
lack  of  saturation  of  ordinary  colors  for,  if  colored  media  were  of 
spectral  purity,  the  variation  in  their  appearance  under  differ- 
ent illuminants  would  be  confined  to  changes  in  brightness  only. 

A  mental  picture  of  the  influence  of  the  illuminant  upon  the 
appearance  of  a  color  is  obtained  by  considering  the  effect  on 
the  entire  range  of  tints  and  shades.  .Tints  of  a  certain  hue 
vary  from  complete  saturation  (spectral  purity)  to  complete 
unsaturation  (white).  As  already  stated  colors  of  spectral 
purity  (which  do  not  exist  among  colored  media)  would  only 
be  altered  in  relative  brightness  by  different  illuminants. 
Whites  assume  the  integral  color  of  the  illuminant  so  that  cer- 
tain tints  lying  between  these  two  extremes  are  maximally 
influenced  in  appearance  by  the  spectral  character  of  the 
illuminant.  To  choose  a  color  which  will  be  most  changeable 
in  appearance  under  different  illuminants  requires  experience 
and  an  acquaintance  with  many  facts  of  color  science.  Medium 
or  light  tints  are  in  general  greatly  influenced  by  the  illuminant. 
Purples  are  excellent  examples  and  the  reader  will  find  it  of 
interest  to  study  the  reasons  for  the  changes  in  appearance 
by  referring  to  Figs.  7  and  9. 

If  the  spectral  characteristic  of  a  pigment,  for  example,  ex- 
tends over  quite  a  range  of  wave-lengths  it  is  seen  on  referring 
to  Fig.  7  that  there  will  be  a  different  distribution  of  the  various 
colored  rays  in  the  light  reflected  under  two  different  illumi- 
nants. Under  such  artificial  illuminants  as  the  tungsten  lamp, 
kerosene  flame  and  some  gas  mantles,  most  colors  will  appear 
"warmer,"  that  is,  more  yellowish  or  reddish  than  under  sun- 
light. Under  skylight  they  will  in  general  appear  more  bluish 
than  under  sunlight.  Under  some  of  the  gas  mantles  which 
emit  a  light  of  a  greenish  tint  the  greens  will  be  accentuated 
and  many  colors  will  appear  more  yellowish  in  color.  Under 


LIGHT  AND  COLOR 


57 


illuminants  having  discontinuous  spectra  such  as  the  mercury- 
vapor  lamps,  the  colors  will  be  more  distorted  and  it  is  more 
difficult  to  predict  the  change.  The  following  are  approximate 
appearances  of  a  few  colors  under  different  illuminants  but 
these  will  not  hold  strictly  for  all  colors  of  the  same  appearance 
to  the  eye  under  a  given  illuminant,  because  of  the  variations  in 
spectral  character  of  colors  which  are  possible  without  a  change 
in  the  appearance  of  the  colors  under  the  given  illuminant. 

THE  INFLUENCE  OF  THE  ILLUMINANT  ON  THE  APPEARANCE  OF  COLORS 


Colored 
media 

Blue 
skylight 

Noon 
sunlight 

Tungsten 
lamp 

Mercury 
arc 

Ultramarine 

Blue 

Greenish-blue 

Darker   ruddy 

Deep  blue 

blue 

Chrome  yellow 

Lemon  yellow 

Golden  yellow 

Orange-yellow 

Greenish-yellow 

Vermilion 

Yellowish-red 

Brick  red 

Red 

Ruddy  gray 

Chrome  green 

Green 

Yellowish-green 

Yellow-green 

Yellowish-green 

Cobalt  blue 

Light  blue 

Light  blue 

Violet 

Violet  blue 

Purple 

Blue 

Reddish-violet 

Red-purple 

Violet 

Pink 

Pink 

Redder  pink 

Light  red 

Light  blue 

Dark  blue 

Blue 

Blue 

Bluish-black 

Violet  blue 

The  appearances  of  pigments,  dyes,  and  glasses  are  so  varied 
and  depend  upon  so  many  factors  that  it  appears  best  to  recom- 
mend that  experience  be  gained  by  actual  experiment.  It  is 
difficult  to  describe  the  changes  in  color  even  in  specific  cases 
but  it  is  easy  to  see  the  magnitude  of  these  changes  by  arranging 
a  series  of  compartments  illuminated  by  common  illuminants. 
By  viewing  specimens  of  the  same  colored  fabric  simultaneously, 
the  importance  of  the  illuminant  will  be  found  to  be  very  great. 
Studies  of  the  effect  of -intensity  in  distinguishing  colors  also 
may  be  carried  out.  Such  a  demonstration  is  extremely  edi- 
fying to  the  user  of  light. 

A  great  deal  of  confusion  arises  in  dealing  with  color  from  the 
inaccurate  and  indefinite  terminology  ordinarily  used.  Before 
proceeding  further  in  the  discussion  of  color  it  is  necessary  to 
define  the  terms  to  be  used.  For  most  scientific  purposes  it  is 
essential  to  use  the  results  of  spectral  analyses  but  a  terminology 
for  everyday  use  need  not  include  terms  for  indicating  the  spec- 
tral characteristics  of  colors.  Ordinarily  we  are  concerned  with 
subjective  color,  that  is,  with  its  appearance  to  the  eye,  so  the 


58  THE  LIGHTING  ART 

most  practicable  terminology  will  provide  terms  which  will 
give  an  idea  of  the  appearance  of  colors. 

It  has  been  found  that  all  colors  except  the  purples  (which 
include  pink,  rose,  and  others  having  dominating  components 
of  red  and  violet)  may  be  matched  by  mixing  monochromatic 
spectral  light  with  white  light.  Purples,  for  which  no  match  in 
hue  is  found  in  the  spectrum,  may  be  analyzed  by  the  same 
process  except  that  a  complementary  hue  is  mixed  with  a  pur- 
ple until  the  mixture  matches  the  standard  white  light.  On 
the  basis  of  this  method  of  colorimetry  it  is  possible  to  define  a 
color  in  terms  of  hue,  saturation  or  purity,  and  luminosity  or 
brightness.  These  are  more  specifically  defined  below  along 
with  other  terms. 

Hue  is  that  property  of  color  by  which  the  various  spectral 
regions  are  characteristically  distinguished.  All  colors  except 
purples  and  white  may  be  matched  in  hue  with  spectral  colors. 
In  the  case  of  a  purple  the  spectral  hue  which  is  complementary 
to  the  hue  of  the  purple  is  ordinarily  used  for  scientific  designa- 
tion. It  is  recognized  that  hue  is  commonly  designated  or  im- 
plied in  the  names  of  colors. 

Two  hues  are  complementary  if  they  may  be  mixed  to  pro- 
duce white.  White  may  be  considered  to  be  a  color  possessing 
no  hue.  By  mixing  two  or  more  hues,  properly  chosen  both  as 
to  hue  and  intensity,  white  may  be  obtained.  Whenever  two 
or  more  hues  are  mixed  the  resultant  color,  though  it  may  still 
have  a  dominant  hue,  will  usually  appear  as  having  an  admix- 
ture of  white.  It  is  interesting  to  arrange  the  spectral  colors 
in  proper  sequence  upon  three-fourths  of  the  circumference  of  a 
circle  and  to  close  the  gap  by  means  of  the  purples.  If  this  is 
properly  done  the  colors  which  lie  at  the  opposite  ends  of  any 
diameter  are  approximately  complementary.  As  an  aid  the 
following  pairs  of  approximately  complementary  colors  are 
given. 

COMPLEMENTARY  HUES 

Violet  and  yellow  Blue-green  and  red 

Blue  and  orange  Green  and  purple 

With  these  as  reference  points  on  the  " color  circle"  other 
complementaries  will  be  readily  found. 


LIGHT  AND  COLOR  59 

Saturation  of  a  color  is  its  degree  of  freedom  from  admixture 
with  white.  Monochromatic  spectral  light  may,  for  purposes  of 
physical  measurements,  be  considered  as  having  a  saturation 
of  100  per  cent.  As  white  is  added  the  saturation  decreases, 
until  when  the  hue  entirely  disappears  the  saturation  is  zero. 
White  is  the  limiting  color  having  no  hue  and  zero  saturation. 

Tints  are  produced  by  the  addition  of  white  to  pure  colors. 
Thus  rose  is  a  tint  of  purple;  cream  is  a  tint  of  yellow;  and  the 
clear  sky  has  a  tint  of  blue. 

Brightness  or  luminosity  of  color  needs  no  special  definition 
but  rather  an  explanation  in  its  relation  to  color.  It  is  that 
which  a  totally  color-blind  eye  sees.  With  colors  we  are  sel- 
dom concerned  with  absolute  values  of  brightness  but  relative 
luminosities  are  important.  For  example,  white  is  only  rela- 
tive with  respect  to  luminosity  or  brightness  for  if  another 
specimen  of  the  same  material  be  illuminated  to  a  lower  inten- 
sity it  will  appear  gray  though  the  first  appears  white.  How- 
ever, if  the  second  specimen  is  illuminated  to  a  higher  intensity 
the  first  will  now  appear  gray  by  comparison  instead  of  white. 
This  is  true  of  the  luminosity  of  any  color.  With  pigments  the 
luminosity  may  be  reduced  by  an  admixture  of  "black." 
An  excellent  term  which  describes  the  brightness  is  "value"  in 
the  sense  used  by  the  artist. 

Shades  of  a  color  are  produced  by  lowering  its  brightness 
which  may  be  done  by  decreasing  the  intensity  of  illumination 
or  by  the  admixture  of  "black"  in  the  case  of  pigments.  For 
example,  olive  green  is  a  shade  of  yellow-green. 

It  is  obvious  that  for  a  given  hue  the  saturation  and  bright- 
ness may  be  altered  separately  or  together  thus  producing  a 
vast  number  of  colors.  The  total  number  of  colors  in  the  broad- 
est sense  including  the  element  of  brightness,  that  may  be  distin- 
guished by  the  human  eye  may  be  estimated  only  approxi- 
mately. Inasmuch  as  only  the  order  of  magnitude  would  be  of 
interest  here,  we  will  set  the  limits  rather  wide,  namely  be- 
tween 100,000  and  1,000,000.  Leaving  luminosity  out  of 
consideration  it  is  likely  that  the  eye  can  distinguish  at  least 
5000  different  tints  under  the  best  experimental  conditions. 


CHAPTER  VIII 
COLORED  ILLUMINANTS 

Colored  illuminants  for  lighting  effects  may  be  divided  into 
two  broad  classes;  namely,  fairly  pure  colors  of  high  satura- 
tion, and  tints  of  low  saturation.  The  purer  colors  have  many 
uses  in  spectacular  illumination,  stage  effects,  advertising  dis- 
plays, signalling  and  other  scientific  applications.  The  tints 
are  chiefly  applicable  for  artistic  purposes  and  it  appears  that 
the  future  will  witness  a  wide  application  of  tinted  illuminants 
as  these  become  more  readily  obtainable  and  as  the  charm  of 
tinted  light  becomes  more  appreciated.  The  mistake  is  often 
made  when  employing  colored  light  for  artistic  purposes  that 
the  hue  is  too  pronounced  for  it  should  be  felt  rather  than 
seen.  The  chief  deterrent  to  the  wider  application  of  color 
in  lighting  is  the  difficulty  of  obtaining  the  desired  colored  light 
for  usually  it  is  necessary  to  obtain  colored  media  and  to  adapt 
them  to  the  light-source  or  accessory. 

The  sources  of  colored  light  for  illuminating  purposes  are 
commercial  illuminants  unaltered  or  equipped  with  colored 
media.  The  commercial  illuminants  afford  a  wide  variety  of 
tints  but  for  practical  considerations  many  of  these  are  barred 
from  the  greater  field  in  interiors  where  the  charm  of  colored 
light  is  beginning  to  be  appreciated.  Before  discussing  the 
various  methods  and  colored  media  available  for  obtaining 
colored  light  for  illuminating  purposes  it  appears  of  interest 
to  discuss  the  colors 'of  common  illuminants  and  a  few  special 
ones  which  may  find  greater  applications  in  the  future. 

Daylight. — Clear  noon  sunlight  may  be  taken  as  a  standard 
white  light  for  the  present  purpose,  although  this  is  an  un- 
settled point.  The  physiologist  and  psychologist  sometimes 
base  the  determination  of  white  light  upon  different  criteria 
than  does  the  physicist.  However,  clear  noon  sunlight  will 
be  considered  as  having  no  hue  and  zero  saturation.  Satura- 

60 


COLORED  ILLUMINANTS  61 

tion  will  be  expressed  in  per  cent.,  and  is  equal,  in  a  given  case, 
to  100  per  cent,  minus  the  per  cent,  white  which  must  be  added 
to  a  spectral  hue  in  order  to  match  the  given  illuminant  in 
color.  Owing  to  the  lack  of  standardization  of  white  light, 
saturations  of  colors  are  not  well  established  so  the  values  in 
the  following  descriptions  will  be  presented  in  round  numbers 
which  represent  only  the  approximate  values.  Clear  blue 
skylight,  which  is  selectively  scattered  sunlight,  has  a  satura- 
tion of  approximately  50  per  cent,  and  its  hue  is  near  0.47/4. 
That  is,  a  mixture  of  about  50  per  cent,  of  monochromatic 
light  of  wave-length  0.47/4  and  50  per  cent,  of  white  light 
produces  a  light  which  matches  clear  blue  skylight  in  color. 
The  means  for  imitating  daylight  in  spectral  character  are 
described  in  another  chapter  but  these  provide  illuminants 
which  simulate  daylight  both  objectively  and  subjectively; 
that  is,  in  spectral  character  as  well  as  in  integral  color  as  it 
appears  to  the  eye.  Only  subjective  color-matches  are  con- 
sidered in  the  present  discussion. 

Electric  Incandescent  Filament  Lamps. — These  illuminants 
range  in  color  from  a  deep  yellowish  tint  for  the  old  " 4- watt" 
carbon  lamp  to  a  yellowish-white  of  the  modern  lamps.  The 
saturation  of  the  "4- watt"  carbon  is  about  80  per  cent.,  and 
its  hue  about  0.595/4.  These  values  for  the  tungsten  vacuum 
lamp  (8  lumens  per  watt)  are  respectively  about  70  and  0.590/4; 
and  for  the  gas-filled  tungsten  lamp  (22  lumens  per  watO 
are  about  55  and  0.585/1.  It  is  seen  that  the  hue  as  expressed 
in  wave-length  of  spectral  light  varies  only  slightly  for  these 
lamps  but  the  saturation  varies  considerably.  A  decrease  in 
saturation  indicates  an  approach  toward  white,  for  white  is 
of  zero  saturation. 

Candle  Flame. — Its  saturation  and  hue  are  respectively  about 
85  per  cent,  and  0.60/4.  This  is  a  very  pleasing  color  for  many 
interiors  where  daylight  appearances  of  colors  are  not  important 
and  it  may  be  obtained  very  readily  and  without  an  excessive 
decrease  in  luminous  efficiency  by  tinting  a  tungsten  lamp  as  will 
be  described  later. 

Mercury  Arc. — The  color  of  the  light 'emitted  by  the  glass- 
tube  arc  is  represented  by  a  saturation  of  about  25  per  cent. 


62  THE  LIGHTING  ART 

and  a  hue  (blue-green)  of  about  0.49/4.  The  quartz  mercury 
arc  is  nearly  a  subjective  white  approaching  zero  saturation. 

Acetylene  Flame. — The  saturation  of  the  light  from  an 
acetylene  flame  is  nearly  the  same  as  that  from  a  tungsten 
vacuum  lamp  operating  at  8  lumens  per  watt,  its  hue  being  in 
the  neighborhood  of  0.585/4. 

Vacuum  Tubes. — The  Moore  carbon-dioxide  tube  emits  a 
light  which  is  a  close  approximation  to  the  ordinary  mixture 
of  skylight  and  direct  sunlight.  The  nitrogen  tube  emits  a 
pink  light  of  moderate  saturation;  the  helium  tube  a  yellowish 
light  of  about  60  per  cent,  saturation  and  a  hue  close  to  0.59/4; 
the  neon  tube  a  light  of  a  decided  orange  hue,  about  0.62/1, 
and  of  high  saturation  of  the  order  of  magnitude  of  90  per  cent. 

Carbon  Arcs. — These  illuminants  vary  widely  in  color  ow- 
ing to  the  various  metals  contained  in  the  impregnating  salts. 
The  crater  of  the  pure  carbon  arc  emits  a  light  of  a  hue  in  the 
vicinity  of  0.58/4  depending  upon  the  current  density.  The 
saturation  is  of  the  order  of  magnitude  of  40  per  cent.  The 
purplish  tint  of  the  pure  carbon  arc  is  due  to  the  arc  and  not  to 
the  crater  for  the  latter  is  yellowish-white.  The  yellow  flam- 
ing arc  emits  bands  of  green  and  red  light  (due  to  calcium) 
superposed  on  a  weaker  continuous  spectrum.  Its  color  is  a 
pronounced  yellow.  The  snow-white  flaming  arc,  whose  car- 
bons are  impregnated  with  rare-earth  compounds,  and  is  said 
to  emit  a  light  which  approximates  a  mixture  of  skylight  and 
direct  sunlight.  The  red  flaming  arc  emits  light  of  a  pinkish- 
red  color  due  chiefly  to  the  yellow  and  red  spectral  lines  emitted 
by  strontium  with  which  the  carbons  are  impregnated. 

Gas  Flames  and  Mantles. — The  color  of  the  light  from  a  gas 
flame  varies  somewhat  but  is  found  in  the  neighborhood  of  a 
kerosene  flame.  The  light  from  incandescent  mantles  varies 
widely  in  color  from  a  greenish  to  a  yellowish  hue. 

Various  transmitting  and  reflecting  media  are  available  for 
altering  the  color  of  illuminants  by  absorbing  some  of  the 
spectral  colors.  Among  these,  colored  glass  is  the  most 
permanent  medium  and  is  available  in  various  forms.  Sheet 
glass  may  be  obtained  in  a  variety  of  colors  but  many  of  these 
have  not  been  made  specially  for  illuminating  purposes  so  that 


COLORED  ILLUMINANTS  63 

some  manipulation  is  usually  necessary.  Signal  lenses  afford 
a  variety,  of  moderately  pure  colors  for  special  purposes,  among 
the  available  colors  being  red,  yellow,  canary,  green,  blue-green, 
blue  and  purple.  The  red  is  usually  sufficiently  pure  for  the 
most  exacting  requirements  of  lighting,  and  the  yellow  and 
canary  are  also  usually  satisfactory.  The  green  may  be  used 
successfully  for  many  purposes  for  which  it  may  be  required 
but  it  may  be  altered  toward  a  yellow-green  by  superposing 
upon  it  a  canary  or  yellow  glass.  Similarly,  it  may  be  altered 
toward  a  bluish-green  by  superposing  a  blue-green  glass.  The 
blue  glasses  are  ordinarily  unsatisfactory  for  some  purposes 
owing  to  the  fact  that  the  cobalt  blue,  which  is  most  common, 
transmits  deep  red  rays.  These  may  be  eliminated  by  super- 
posing a  blue-green  (copper)  glass.  Purple  has  few  uses  in 
lighting  but  pink  is  often  desirable.  A  beautiful  pink  glass  is 
obtainable  by  incorporating  gold  in  glass.  Further  possibilities 
in  combining  colored  glasses  may  be  realized  from  a  knowledge 
of  the  principles  of  color  which  are  involved.1 

Glass  caps  are  available  in  several  colors  and  some  incandes- 
cent lamps  are  made  with  colored  glass  bulbs,  among  them  being 
red,  yellow,  canary,  green,  and  blue.  Future  demands  will 
doubtless  result  in  the  availability  of  purer  colors  and  various 
tints. 

Illuminating  glassware  provides  some  possibilities  for  ob- 
taining colored  light  especially  the  deep  glass  shades  and  en- 
closing units  which  are  colored.  If  a  tinted  light  is  desired  for 
general  illumination  an  enclosing  unit  is  usually  essential. 
Even  with  the  pendant  shades  and  inverted  glass  bowls  beau- 
tiful effects  may  be  obtained  by  so  devising  the  unit  that  the 
light  which  is  tinted  by  transmission  through  the  colored  glass 
will  fall  on  the  desired  places  and  the  unaltered  light  which  es- 
capes directly  will  serve  the  purpose  of  general  illumination. 
A  reverse  effect  is  obtained  in  such  a  case  as  a  shower  equipped 
with  yellow  pendant  shades.  If  this  is  placed  over  a  dining 
table  the  faces  of  the  diners  and  the  surroundings  are  lighted  by 


1  M.  LUCKIESH:  "The  Physical  Basis  of  Color-Technology,"  Jour.  Frank. 
Inst.,    1917,  vol.  182,  p.  73,  227. 


64  THE  LIGHTING  ART 

the  warm  tint  and  the  predominant  light  on  the  table  is  unal- 
tered in  color. 

Silk  and  other  textiles  are  readily  obtained  of  suitable  colors 
and  may  be  applied  to  lighting  units  with  ease.  These  not 
only  may  be  selected  to  harmonize  with  the  decorative  color- 
scheme  but  the  light  transmitted  and  reflected  by  the  colored 
fabric  lends  the  charm  of  color  so  enjoyable  in  many  interiors. 
Colored  gelatines  are  also  available  in  a  vast  variety  of  tints 
but  these  are  not  very  permanent  in  color.  They  will  not'  fade 
very  rapidly  under  exposure  to  moderate  intensities  of  illumi- 

c    nation  but  deteriorate  rapidly  if  allowed  to 

B    become  hot .     The  yellows  are  in  general  the 

least  fugitive. 

Colored   lacquers   for  dipping  lamps   are 
available  in  a  variety   of   colors  including 
pink,  red,  deep  amber,  canary,  green,  blue- 
green,  and  blue.     Their  chief  disadvantage 
FIG.  s.^Method  of   is   lack    of   permanency  but  they   are  less 
increasing  the  life  of    fugitive  under  exposure  to  moderate  light  if 

colored  screens.  .  . 

the  temperature  is  not  too  high  than  when 
exposed  to  intense  heat  and  light.  The  coloring  elements  are 
usually  dyes  as  is  true  of  the  gelatines.  It  is  often  ad- 
vantageous to  use  these  dyed  gelatines  or  lacquers  on 
glass  or  mica  separated  from  the  light-source  by  an  air- 
space. A  clear  glass  may  be  interposed  between  such 
colored  filters  and  the  light-source  which,  by  absorbing 
some  of  the  infra-red  energy  and  by  providing  an  air-space, 
greatly  prolongs  the  life  of  the  colored  niters.  A  re- 
finement of  this  scheme  is  to  use  in  place  of  the  clear  glass  a 
colored  glass  of  almost  the  desired  color.  This  absorbs  even 
more  of  the  undesired  energy  than  clear  glass,  and  the  dyed  filter 
may  be  depended  upon  only  for  the  final  color-correction.  One 
scheme  is  shown  in  Fig.  8  where  A  is  a  heat-resisting  glass,  B 
is  the  colored  glass  of  approximately  the  desired  color,  and  C 
is  the  final  correcting  filter  in  which  comparatively  fugitive  dyes 
may  be  used  with  fair  satisfaction.  A  water-cell  is  very  effect- 
ive in  absorbing  the  infra-red  energy  and  therefore  has  been 
used  for  such  purposes. 


COLORED  ILLUMINANTS  65 

An  advantage  of  colored  lacquers  is  that  they  may  be  readily 
mixed,  diluted,  and  applied,  thus  affording  an  easy  means  for 
obtaining  many  desired  colors  of  light.  Many  red  dyes  in 
weak  concentrations  are  pink  in  color  so  that  a  red  lacquer  may 
be  diluted  with  uncolored  lacquer  in  order  to  obtain  pink.  It 
is  well  to  distinguish  between  the  clear  lacquer  and  the  thinner 
or  solvent.  If  the  latter  is  used  the  lacquer  may  become  so 
dilute  as  to  lose  its  binding  qualities.  Many  of  these  lacquers 
consist  of  a  solution  of  celluloid  in  alcohol,  ether,  amyl  acetate, 
acetone,  etc.,  but  generally  they  are  not  weather-proof.  Var- 
nishes withstand  the  elements  outdoors  fairly  well  and  shellac 
has  value  as  a  lacquer  for  dyeing.  Solutions  of  yellow  dyes  of 
low  concentrations  are  generally  greenish-yellow  in  color  so  that 
if  a  warm  tint  of  yellow,  which  simulates  the  old  illuminants,  is 
desired  an  addition  of  pink  is  necessary.  This  absorbs  rays  in 
the  middle  of  the  spectrum,  namely  in  the  yellow-green  region. 
Green  lacquers  which  do  not  transmit  red  rays  are  relatively 
rare.  Those  which  transmit  a  deep  red  band  may  be  corrected 
to  a  satisfactory  green  by  adding  blue-green  dye  provided  the 
blue-green  does  not  transmit  these  red  rays.  Moonlight  is 
usually  simulated  by  using  a  greenish-blue  filter  of  a  fairly 
unsaturated  tint  over  such  an  illuminant  as  the  tungsten  lamp 
although  the  spectral  character  of  moonlight  in  reality  closely 
approximates  that  of  sunlight.  This  " moonlight"  blue  may 
be  made  by  mixing  weak  solutions  of  blue  and  green  or  by  add- 
ing blue  to  an  unsaturated  blue-green  lacquer.  Solutions  of 
blue  dyes  which  do  not  transmit  deep  red  rays  are  very  rare 
but  usually  a  fairly  satisfactory  deep  blue  filter  may  be  made 
by  adding  blue-green  to  the  blue  lacquer.  Purple  may  be 
obtained  in  any  depth  of  color  by  adding  pink  and  blue  to  a 
clear  lacquer.  Many  dilute  reds  provide  satisfactory  pinks. 

Many  pigments  are  quite  permanent  but  these  are  insoluble 
and  are  more  difficult  of  application.  The  author  has  used 
these  successfully  for  some  purposes  by  developing  a  special 
method  of  application.  Tinted  light  may  be  obtained  by  select- 
ive reflection  from  colored  surfaces  and  for  this  purpose  pig- 
ments serve  very  well.  For  example,  the  inner  surface  of  an 
opaque  reflector  may  be  colored  with  a  paint  made  by  suspend- 


66  THE  LIGHTING  ART 

ing  the  pigment  in  a  suitable  vehicle.  Where  the  surface  is  not 
exposed  to  intense  heat,  varnish,  shellac,  and  celluloid  lacquer 
are  satisfactory.  Such  pigments  may  be  applied  to  any  sur- 
faces which  may  be  depended  upon  to  supply  the  colored  light 
by  selective  reflection  but  a  rough  surface  is  best. 

For  temporary  lighting  effects  even  aqueous  solutions  of  dyes, 
metallic  salts,  etc.,  find  application  and  beautiful  effects  may 
be  obtained  by  permitting  colored  salts  to  crystallize  on  trans- 
parent or  translucent  surfaces.  Gelatine  filters  may  be  made 
by  dissolving  a  dye  in  a  warm  6  per  cent,  aqueous  solution  of 
gelatine.  This  colored  solution  may  be  flowed  upon  level  glass 
and  when  dry  excellent  color  filters  are  available.  Colored 
lacquers  may  also  be  flowed  upon  level  glass  and  allowed  to  dry. 
If  a  diffusing  colored  screen  is  desired  it  is  possible  to  dye  an 
opal  lacquer  or  a  temporary  filter  may  be  made  by  dyeing  a  warm 
saturated  aqueous  solution  of  epsom  salts.  After  the  latter  has 
dried  upon  glass  an  effect  similar  to  frosted  colored  glass  is 
obtained.  This  will  not  withstand  heating  because  the  crys- 
tals will  fuse  at  a  moderate  temperature.  These  are  some  of 
the  ways  of  devising  filters  for  obtaining  light  of  desired  colors 
which  have  been  found  useful  by  experience. 

For  obtaining  daylight  effects  various  units  are  available 
which  simulate  in  spectral  character,  north  skylight,  noon- 
sunlight,  and  approximate  sunlight.  These  are  discussed  in  a 
separate  chapter  owing  to  their  wide  application. 

Light  of  any  desired  color  may  be  obtained  by  applying  other 
methods  of  color-mixture.  In  preceding  paragraphs  of  this 
chapter  it  has  been  shown  how  an  illuminant  could  be  altered  by 
selective  reflection  and  transmission.  In  order  to  apply  this 
subtractive  method  with  certainty  as  to  the  results,  knowledge 
must  be  had  of  the  spectral  characteristics  of  the  colored  media 
and  of  the  color  which  remains  when  certain  colored  rays  have 
been  subtracted  or  absorbed.  An  inexpensive  pocket  spectro- 
scope is  a  valuable  aid  in  such  work  and  adds  much  to  the  inter- 
est in  the  application  of  color  to  lighting. 

It  is  helpful  in  obtaining  colored  light  by  the  subtractive 
method,  that  is,  by  superposing  colored  glasses,  mixing  colored 
lacquers,  etc.,  to  consider  the  primaries  to  be  purple,  yellow, 


COLORED  ILLUMINANTS  67 

and  blue-green.  Such  combinations  or  mixtures  transmit  only 
those  colored  rays  which  they  transmit  in  common.  For  ex- 
ample, a  purple  filter  superposed  on  a  yellow  one  results  in  a 
red  filter;  a  mixture  of  yellow  and  blue-green  paints  results  in 
green  paint;  and  a  blue-green  glass  superposed  on  a  purple  one 
results  in  a  violet  or  blue  transmission.  If  the  spectral  curves 
be  drawn  for  these  subtractive  primaries  the  sub  tractive  method 
is  seen  more  clearly.  These  are  shown  diagrammatically  in 
Fig.  9  where  the  vertical  heights  of  the  full  lines  represent  spec- 


PURPLE 

N 

S~ 

'\^ 

YELLOW 

f           „  —  ^ 

**                          ** 

/          \ 

BLUE-  GREEN 

^> 

/^ 

.49*6        0.45             0.5 
V             B                  G 

0              0.55              0.60             0.65            0.7 
Y                   0                R 

WAVE  -  LENGTH    AND    HUE 
FIG.  9. — Diagrammatic  illustration  of  'subtractive'  primary  colors. 

tral  transmission-  or  reflection-factors  for  energy  of  various 
wave-lengths.  The  dotted  lines  represent  the  corresponding 
spectral  luminosities  for  a  given  illuminant.  It  is  easy  to  note 
the  rays  which  any  pair  transmit  in  common  and  that  the  three 
superposed  result  in  zero  transmission.  From  a  study  of  this 
method  it  should  be  possible  to  employ  any  colors  in  subtractive 
mixtures  with  a  fairly  definite  prediction  as  to  the  results  to  be 
expected.  If  illuminants  possessing  continuous  spectra  are 
used  the  table  of  complementary  colors  and  the  "color  circle" 
presented  in  Chapter  VII  will  be  found  helpful  in  predicting  the 
results  of  selective  absorption.  The  best  way  in  which  to 
acquire  a  general  knowledge  of  the  manipulation  of  colored 


68 


THE  LIGHTING  ART 


media  is  by  experience  with  them  and  the  subject  should  be 
sufficiently  interesting  and  attractive  to  pursue  with  pleasure. 
An  extensive  treatment  of  color  and  its  applications  has  re- 
cently been  published1  for  those  who  wish  to  go  deeper  into  the 
subject  and  to  avail  themselves  of  the  manifold  possibilities  of 
color  in  lighting. 

It  has  long  been  known  that,  by  mixing  three  primary 
colored  lights,  namely  red,  green,  and  blue,  any  desired  hue 
may  be  obtained.  Although  this  fact  has  been  known  to 


FIG. 


0.80 
0.60 
0.40 
0.20 

°0 

/ 

"  R 

"^ 

B 

G 

N 

I/ 

\ 

y 

7 

\ 

/ 

y 

\ 

I 

/ 

A 

\ 

\ 

1 

49^        0.45            0.50            0.55            0.60           0.65           0.7 
V              B               G                Y                OR 

WAVE -LENGTH    AND    HUE 

10. — Spectral  characteristics  of  three  practicable  'additive'  primary  color- 


science  for  many  years,  it  has  been  rarely  applied  in  lighting 
effects.  Its  widest  field  of  application  is  in  stage-lighting  and 
in  spectacular  effects  though  it  has  many  other  applications, 
some  of  which  have  been  mentioned  in  other  chapters.  Various 
sets  of  these  primary  colors  are  satisfactory  for  most  purposes, 
but  the  author  has  found  the  following  to  be  very  generally 
satisfactory  for  lighting  effects: 

A  red  light  whose  spectral  limits  are  about  o.6o/x  and  the 
end  of  the  visible  spectrum,  and  whose  dominant  hue  is  near 
o.66/i.  This  is  a  fairly  saturated  red. 

A  green  light  of  a  yellowish  tinge  whose  spectral  limits  are 
about  0.46/4  and  0.57/4,  and  whose  dominant  hue  is  near  0.54/4. 

A  blue  light  which  contains  no  red  rays,  whose  spectral 

1  M.  LUCKIESH:  "Color  and  Its  Applications,"  1916. 


COLORED  ILLUMINANTS  69 

limits  are  about  0.51/11  and  the  end  of  the  visible  spectrum,  and 
whose  dominant  hue  is  near  0.45^1. 

The  special  transmission-factors  of  three  colored  media  in 
the  filters  employed  satisfactorily  for  many  lighting  effects  are 
shown  in  Fig.  10.  These  were  chosen  for  practicability  as  to 
transparency,  permanency,  ease  of  reproducibility,  as  well  as 
to  color.  They  are  obtained  by  dyeing  lacquers  but  it  is 
hoped  that  they  will  be  available  eventually  in  glass.  It  is 
possible  to  obtain  satisfactory  combinations  of  colored  glass 
in  the  market  for  producing  these  primary  colored  lights  but 
difficulties  must  be  overcome  in  combining  them  and  in  using 
them  in  a  practicable  manner.  Quite  a  variety  of  satura- 
tions of  two  different  hues  are  obtainable  from  mixtures  of 
two  complementary  colored  lights.  Although  the  variety  of 
colors  is  limited,  this  procedure  finds  applications  in  lighting. 

The  simplest  means  of  mixing  colors  in  this  manner  is 
usually  by  rheostatic  control  although  the  color  of  the  light 
emitted  by  the  light-source  changes  with  the  current  and  there- 
fore the  primary  colors  are  altered.  However,  the  change  in 
the  latter  is  comparatively  slight  and  usually  unimportant. 
Movable  templates  are  simple  expedients  which  may  be  utilized. 
These  methods  of  control  are  discussed  in  another  chapter. 

Another  method  of  mixing  colored  lights  for  obtaining  de- 
sired tints  is  to  juxtapose  the  filters  or  to  arrange  them  in 
checkerboard  fashion.  For  example  if  a  "warm"  yellow  tint 
is  desired  it  is  almost  impossible  to  obtain  this  by  means  of  a 
single  coloring  element  and  an  ordinary  illuminant  because 
such  yellows  are  usually  amber  in  color  which  in  the  lighter  tints 
is  a  greenish-yellow.  Dense  amber  has  a  dominant  hue  in 
the  yellow  region  of  the  spectrum  but  it  is  of  high  saturation. 
If  a  few  pieces  of  dense  amber  glass  be  placed  upon  a  diffusing 
uncolored  glass,  the  resultant  light  from  a  tungsten  lamp  or 
similar  illuminant  will  be  of  the  desired  warm  yellow  hue.  The 
resultant  light  consists  of  a  mixture  of  the  unaltered  light  with 
the  deep  yellow  light.  The  diffusing  glass  mixes  the  lights  so 
that  the  effect  is  uniform  if  the  receiving  areas  are  sufficiently 
distant.  Various  tints  may  be  obtained  from  the  ordinary 
colored  glasses  which  are  available. 


70  THE  LIGHTING  ART 

Another  example  is  that  of  a  rose  tint  which  may  be  obtained 
by  placing  small  pieces  of  blue  and  red  glass  over  the  diffusing 
glass.  The  saturation  of  the  resultant  colored  light  is  con- 
trolled chiefly  by  varying  the  percentage  of  the  area  of  the 
diffusing  glass  not  covered  by  the  pieces  of  colored  glass,  and 
the  hue  by  varying  the  relative  areas  of  blue  and  red  glasses. 
The  method  is  simple  as  shown  in  Fig.  n.  These  checker- 
board niters  may  be  used  as  shown  in  Fig.  8  in  order  to  prolong 
their  life  if  the  coloring  material  is  not  permanent.  Daubs 


Yellow  Tirrf-  Pink    Tirrh 

FIG.   n. — Simple  method  of  obtaining  desired  tint  of  light 

of  different  colored  lacquers  upon  diffusing  glass  are  equally 
effective  but  not  as  permanent.  Heat-resisting  glass  which  has 
been  sand-blasted,  on  both  sides  if  necessary  in  order  to  obtain 
sufficient  diffusion,  may  be  advantageously  utilized  for  such 
purposes. 

The  principles  of  color-mixture  with  which  the  lighting 
specialist  should  be  acquainted  have  been  discussed  in  this 
chapter  and  many  practicable  means  of  utilizing  colored  media 
have  been  presented.  The  lighting  specialist  today  usually 
must  gather  the  materials  for  obtaining  colored  light  and  have 
the  apparatus  constructed.  There  is  some  stage-lighting  and 
other  equipment  available  for  a  few  applications  but  the  future 
will  doubtless  find  that  lamps  and  accessories  will  be  available 
in  greater  variety  for  applying  colored  light. 


CHAPTER  IX 
THE  PSYCHO-PHYSIOLOGY  OF  COLOR 

There  are  so  many  variables  in  the  problems  of  color  in 
lighting  that  no  simple  rules  of  procedure  can  be  formulated 
and  therefore  it  is  necessary  for  the  lighting  specialist  to  be 
acquainted  in  a  general  manner  with  various  aspects  of  color. 
Some  phenomena  in  lighting  remain  mysteries  and  opportuni- 
ties for  achievements  are  lost  to  those  unacquainted  with  the 
physiological  and  psychological  aspects  of  vision  and  with  the 
effects  of  brightness  and  color  upon  the  human  organism.  No 
attempt  will  be  made  to  describe  the  various  theories  of  color- 
vision  or  to  explain  many  of  the  phenomena  encountered  in  the 
use  of  colored  light  because  this  would  lead  far  afield.  How- 
ever, some  of  the  more  important  aspects  will  be  touched  upon 
in  order  that  those  interested  in  lighting  may  be  aided  in 
seeking  explanations  from  those  sources  which  are  devoted 
specifically  to  the  treatment  of  the  questions  involved. 

The  importance  of  color-vision  is  not  comparable  with  that 
of  colorless-vision  because  the  totally  color-blind  person  is  not 
greatly  handicapped  in  pursuing  the  ordinary  activities  of  life 
except  those  in  which  man  has  used  color  for  special  services. 
However,  color-vision  is  a  wonderful  gift  capable  of  adding  to 
the  variety  of  our  experiences  and,  having  this  faculty,  it 
should  be  utilized  not  only  for  technical  purposes  but  for  adding 
to  the  interest  and  charm  of  our  surroundings.  Many  hypoth- 
eses of  color-vision  have  been  advanced  but  none  is  in  com- 
plete accord  with  experimental  data,  although  the  latter  may  be 
at  fault.  Nevertheless  the  attention  of  scientists  is  directed 
chiefly  toward  two  hypotheses,  namely,  that  of  Young-Helm- 
holtz  and  that  of  Hering.  The  former,  which  was  founded 
largely  upon  the  physical  basis  of  color-mixture,  assumes  the 
presence  of  three  processes.  It  is  supposed  that  these  are 
responsible  for  red,  green,  and  blue  sensations  respectively, 

6  71 


72  THE  LIGHTING  ART 

and  that  any  color  is  the  result  of  simultaneously  arousing  these 
three  sensations  of  different  degrees  quite  analogous  to  the 
results  of  mixtures  of  the  three  primary  colors. 

The  Hering  theory  is  based  more  upon  a  psychological  foun- 
dation, the  chief  fact  being  the  conspicuousness  of  red,  yellow, 
green,  blue,  white,  and  black.  Three  processes  are  assumed  to 
exist,  each  accounting  for  one  of  the  following  pairs  of  color- 
sensations,  namely  red  and  green,  yellow  and  blue,  white  and 
black.  There  is  no  anatomical  evidence  available  as  yet  which 
indicates  the  existence  of  the  three  processes  required  by  either 
of  the  foregoing  hypotheses  but  Von  Kries,  from  such  evidence, 
advanced  the  "rod  and  cone"  theory  which  is  supported  very 
well  by  many  experimental  observations.  Minute  "rods"  and 
"cones"  are  found  to  exist  in  the  retina  and  the  former  are 
apparently  responsible  for  achromatic  sensations  at  low  inten- 
sities. The  cones  seem  to  be  responsible  for  both  achromatic 
and  chromatic  sensations  at  higher  intensities  but  appear  to 
cease  to  function  at  twilight  intensities.  Although  this  theory 
explains  certain  visual  phenomena  very  nicely,  it  does  not  at- 
tempt a  broad  explanation  of  color-vision  as  does  either  of  the 
other  hypotheses  already  mentioned. 

The  hypotheses  of  Ladd-Franklin  and  Edridge- Green,  as 
well  as  others,  are  worthy  of  consideration  but  a  discussion  of 
theories  of  color- vision  is  beyond  the  scope  of  this  volume.  The 
chief  object  has  been  to  warn  those  not  particularly  acquainted 
with  the  subject  that  there  are  many  hypotheses,  none  of  which 
is  accepted  completely,  so  that  they  may  not  be  bound  too  closely 
to  any  one  of  them  at  the  present  time. 

Perhaps  the  most  important  aspect  of  color  is  that  of  con- 
trast. In  fact,  contrast  in  hue  is  the  life  of  color  and  the  ab- 
sence of  it  is  practically  fatal.  For  example,  if  a  red  spot  be 
surrounded  by  white,  the  red  is  much  less  striking  than  when 
surrounded  by  green.  Furthermore,  when  a  room  is  lighted 
with  a  colored  light  of  high  saturation  there  appears  to  be  a 
variety  of  shades  of  approximately  the  same  hue.  There  is 
little  life  to  the  colors  and  gradually  the  impression  of  color 
dwindles.  But  when  the  illuminant  is  changed  to  one  emitting 
rays  of  all  visible  wave-lengths,  the  different  colors  spring  into 


THE  PSYCHO-PHYSIOLOGY  OF  COLOR  73 

life  and  their  contrasts  mutually  reinforce  each  other.  Owing 
to  these  contrasts  the  scene  becomes  alive  with  color. 

The  phenomenon  of  simultaneous  contrast  may  be  divided 
into  two  parts,  namely,  hue-contrast  and  brightness-contrast. 
These  two  are  usually  operating  simultaneously  so  that  it 
requires  close  analysis  and  experimentation  to  diagnose  a  given 
case.  When  a  medium  shade,  such  as  gray,  is  viewed  on  a  dark 
background  it  appears  to  be  a  much  lighter  shade  than  when 
viewed  upon  a  white  background.  Usually  when  two  colors 
are  juxtaposed  they  appear  to  move  farther  apart  in  hue  than 
when  separated  and  viewed  successively.  When  a  color  is 
viewed  against  a  white  background  or  vice  versa,  there  is  gen- 
erally induced  in  the  white  ground,  a  tint  which  is  approxi- 
mately complementary  to  the  inducing  color. 

In  the  case  of  juxtaposed  colors  the  phenomenon  of  successive 
contrast  appears;  that  is,  the  effect  upon  the  appearance  of  a 
color  of  viewing  another  color  immediately  before.  Usually  the 
effect  is  to  enhance  the  appearance  of  colors.  Such  a  condition 
always  exists  when  the  eye  is  roving  over  any  scene  but  it  is 
easier  to  note  the  effect  with  bright  and  fairly  pure  colors. 
After  viewing  a  color  for  a  few  moments,  if  the  eyes  are  suddenly 
turned  to  a  white  surface,  a  colored  after-image  of  the  colored 
object  is  seen  upon  the  white  background.  Usually  the  after- 
image is  approximately  complementary  to  the  original  color. 
These  phenomena  of  contrast  play  a  large  part  in  nearly  all 
color  effects  and  should  be  studied  and  taken  into  account  in 
color-schemes. 

As  indicated  by  the  existence  of  after-images,  color  sensations 
do  not  decay  instantly  on  the  cessation  of  the  stimulus.  It  has 
been  found  that  they  do  not  rise  instantly  to  full  value  and  that 
there  is  an  "  overshooting "  beyond  the  final  value  of  the  sensa- 
tion. Furthermore,  the  rates  of  growth  and  decay  differ  for 
the  various  color  sensations. 

A  phenomenon  which  is  sometimes  of  importance  is  that 
known  as  the  Purkinje  effect.  At  low  intensities  of  illumina- 
tion the  retina  is  relatively  more  sensitive  to  radiant  energy  of 
the  shorter  wave-lengths,  such  as  violet,  blue,  and  green,  than 
at  high  intensities.  For  example,  if  two  colors  such  as  blue 


74  THE  LIGHTING  ART 

and  orange  appear  of  equal  brightness  at  high  intensities  of 
illumination,  the  blue  will  appear  considerably  brighter  than 
the  orange  when  the  intensity  is  reduced  to  a  low  value. 

Different  zones  of  the  retina  vary  in  their  sensitivity  to 
colors,  depending,  however,  upon  many  factors  such  as  bright- 
ness and  size  of  the  retinal  images  of  the  colored  objects.  The 
peripheral  retina  is  practically  insensitive  to  color  but  it  is 
sensitive  to  brightness.  The  minimum  perceptible  brightness- 
difference  is  about  the  same  for  all  colors  at  high  illumination 
but  varies  considerably  for  different  colors  at  low  intensities 
of  illumination. 

Visual  acuity  is  better  in  monochromatic  light  than  in  light  of 
extended  spectral  character;  however,  this  advantage  has  not 
found  wide  practical  application.  It  is  the  opinion  of  many, 
based  upon  general  experience  but  not  on  quantitative  experi- 
mental data,  that  the  eye  is  less  fatigued  under  an  illuminant 
containing  energy  of  all  wave-lengths.  The  mercury  arc  emits 
light  approaching  monochromatism  more  closely  than  other 
common  illuminants  and  minute  details  at  the  threshold  of 
discrimination  are  seen  more  distinctly  under  this  illuminant 
than  under  others;  however,  this  advantage,  which  arises  from 
the  chromatic  aberration  of  the  eye,  decreases  in  magnitude 
for  ordinary  vision  because  the  eye  is  not  ordinarily  engaged 
in  the  perception  of  minute  details  bordering  upon  the  limit  of 
discrimination.  These  are  a  few  facts  which  are  pertinent  in 
lighting  especially,  when  it  is  considered  to  be  as  broad  in  scope 
as  visual  activities.  These  phenomena  and  many  others  will 
be  found  treated  elsewhere  in  greater  detail. 

Relatively  little  is  known  regarding  the  physiological  and 
psychological  effects  of  color  upon  the  human  organism.  Some 
of  these  effects  have  been  investigated  but  much  work  remains 
to  be  done.  Conclusions  along  these  lines  at  present  must 
depend  largely  upon  experience  and  the  knowledge  unearthed 
in  many  fields.  Regarding  such  effects  and  the  esthetics  of 
color,  few  data  of  a  definite  character  based  upon  scientific 
research  are  available  but  there  is  some  degree  of  definiteness 
attainable  by  combining  with  these,  the  knowledge  gained  by 
experience. 


THE  PSYCHO-PHYSIOLOGY  OF  COLOR  75 

One  of  the  most  vulnerable  points  of  attacking  the  psychology 
of  color  is  that  of  color-preference.  Several  scientists  have 
investigated  this  aspect  of  color  and  when  all  influences  and 
associations  are  excluded  as  completely  as  possible  and  the 
colors  are  chosen  for  ''color's  sake"  alone,  it  appears  that  pure 
colors  are  decidedly  more  preferred  than  tints  and  shades. 
Furthermore,  there  is  a  decided  preference  in  general,  in  the 
case  of  pure  colors,  for  those  having  hues  near  the  ends  of  the 
spectrum,  namely,  blue  and  red.  There  is  some  evidence  that 
the  color  most  preferred  by  men  is  blue  and  by  women  is  red 
although  the  results  are  not  sufficiently  conclusive  and  the 
influences  are  too  manifold  to  warrant  a  final  decision.  It  is 
strange  that,  when  the  preference  is  investigated  on  the  basis  of 
"color's  sake,"  the  least-preferred  colors  lie  near  the  middle  of 
the  spectrum;  that  is,  near  the  yellow,  because  this  is  quite 
contrary  to  the  preference  exhibited  in  the  choice  of  colors  in 
decoration.  The  colors  most  generally  used  about  us  for  per- 
manent decoration  are  tints  and  shades  possessing  hues  pre- 
dominantly near  the  yellow  of  the  spectrum  but  on  the  fore- 
going basis  these  are  in  general  the  least  preferred.  Though 
such  information  may  have  its  value  in  lighting  and  certainly 
does  have  its  place  in  the  applications  of  color,  it  must  be  used 
with  caution.  The  contradiction  noted  in  the  foregoing  may  be 
explained  by  assuming  that  the  momentary  delight  in  viewing 
the  colors  more  rarely  used  in  large  proportion  for  permanent 
decoration,  sways  the  judgment  in  favor  of  them  when  associ- 
ations are  eliminated  as  completely  as  possible.  The  fact  that 
we  do  not  accept  these  colors  in  large  proportions  to  live  with 
permanently  indicates  that  the  time-element  is  a  factor. 

Investigations  in  various  publications  of  the  use  of  colors 
in  advertising,  indicates  that  red  is  used  very  much  more  than 
any  other  color  with  the  exception,  of  course,  of  white  and 
black.  Experiments  on  the  attention-value  of  colors  indicates 
that  characters  printed  in  red  attract  the  attention  much  more 
than  those  in  black  when  both  are  viewed  simultaneously. 
By  exposing  different  colors  to  view  on  a  white  ground  for  a 
very  brief  period  such  colors  as  red,  black,  green,  and  orange 
appear  to  be  noticed  more  generally  than  other  colors.  Of 


76  THE  LIGHTING  ART 

course,  there  are  many  factors  which  must  be  considered  and 
the  application  of  the  meager  results  available  must  be  made 
with  caution;  however,  the  results  obtained  in  the  study  of 
various  aspects  of  the  psychology  of  color  seem  to  correlate 
fairly  well. 

There  is  a  general  agreement  in  classifying  colors  into  warm, 
neutral,  and  cold  groups.  These  attributes  seem  to  be  applic- 
able to  the  colors  of  the  spectrum  in  a  definite  manner.  The 
cold  colors  are  those  near  the  blue  end  of  the  spectrum;  the 
neutral  are  found  near  the  middle  in  the  neighborhood  of  green; 
and  the  warm  colors  are  in  the  region  of  yellow,  orange,  and  red. 
Neutrality  appears  to  be  approached  again  near  the  extreme 
ends  of  the  spectrum  and  in  mixtures  of  these,  namely,  the 
purples. 

The  attributes  which  are  bestowed  upon  colors  arise  from 
various  causes  and  a  color  may  be  agreeable  under  a  given  en- 
vironment or  attitude  of  mind  and  quite  unpleasant  under  other 
conditions.  The  judgment  may  be  based  upon  the  appear- 
ance of  the  color  as  to  brightness,  saturation,  etc.;  upon  the 
physiological  effect  such  as  stimulating,  soothing,  heating, 
etc.;  upon  association  such  as  mentally  applying  it  to  some  por- 
tion of  wearing  apparel;  and  upon  the  "character"  or  expression 
of  the  color.  The  last  is  the  most  complex  and  represents  the 
highest  cultivation  in  the  appreciation  of  color.  Those  who 
have  cultivated  this  type  of  appreciation  of  color  are  the  least 
of  all  influenced  by  associations.  Their  appreciation  of  color 
is  essentially  emotional  and  may  be  said  to  be  esthetic  in  the 
highest  sense.  There  is  no  doubt  as  to  the  growth  of  our 
liking  or  disliking  for  certain  colors. 

The  following  are  a  few  attributes  which  have  been  applied 
to  some  of  the  principal  colors  and  which  under  many  conditions 
appear  to  be  appropriate. 

Red — warm,  exciting,  passionate. 

Orange — warm,  exciting,  suffocating,  glowing,  lively. 

Yellow — warm,  exciting,  joyous,  gay,  merry. 

Yellow- green — cheerful. 

Green — neutral,  tranquil,  peaceful,  soothing. 

Blue-green— sober,  sedate. 


THE  PSYCHO-PHYSIOLOGY  OF  COLOR  77 

Blue — cold,  grave,  tranquil,  serene. 

Violet — solemn,  melancholy,  neutral,  depressing. 

Purple — neutral,  solemn,  stately,  pompous,  impressive. 

Though  it  is  difficult  and  perhaps  unwise  to  stamp  the  various 
colors  with  the  attributes  which  they  seem  to  possess  owing  to 
the  influences  of  many  factors,  it  is  certain  that  the  study  of 
color  as  it  has  appealed  to  many  types  of  individuals  of  all 
degrees  of  civilization  reveals  an  expression  or  language  of  color 
which  is  more  or  less  definite.  There  are  many  sources  of  such 
information,  such  as  mythology,  primitive  language,  ecclesias- 
ticism,  poetry,  painting,  and  nature,  and  there  are  some 
accepted  general  principles  pertaining  to  the  harmony  and 
esthetics  of  color.  From  a  study  of  the  employment  of  color 
in  these  various  fields  one  is  convinced  of  the  potentiality  of 
color. 

Perhaps  the  attributes  of  coldness,  warmth,  and  neutrality 
of  colors  are  more  generally  noticed  and  are  used  more  de- 
signedly in  decoration  and  furnishings  than  any  others.  A 
room  with  northern  exposure  may  be  relieved  of  its  coldness 
by  a  proper  choice  of  color.  The  skylight  which  enters  the 
windows  may  be  changed  to  a  yellowish  hue  by  filtering  through 
shades  or  hangings  of  warm  tints  and  the  surroundings  will 
appear  more  cheerful.  The  general  color-scheme  in  wall- 
coverings and  furnishings  often  should  be  one  which  leans 
toward  the  warm  colors  for  rooms  of  northern  exposure. 
However,  in  many  cases,  especially  in  hot  climes,  the  colder 
colors  may  be  used  in  rooms  of  southern  exposure  and  even  in 
those  of  northern  exposure.  In  rooms  of  northern  exposure, 
daylight  openings  may  be  glazed  with  glass  possessing  a  tint  of 
warm  yellow.  Such  glass  is  rare  but  it  is  to  be  found  in  the 
market  at  times.  Weak  tints  of  amber  or  canary  are  readily 
obtainable  in  glass  but  these  are  usually  far  from  satisfactory 
owing  to  their  greenish  tinge  and  conspicuousness  as  colors. 
A  warm  yellow  tint  will  be  practically  unnoticed  where  a  lemon 
yellow  of  equal  saturation  and  brightness  will  appear  con- 
spicuously colored  when  these  are  associated  with  illuminants. 

In  artificial  lighting  the  color  of  the  luminous  portions  of 
the  lighting  unit  is  likely  to  influence  the  impression  far  more 


78  THE  LIGHTING  ART 

than  the  actual  color  of  the  light  which  illuminates  the  sur- 
roundings. For  example,  if  a  direct-indirect  luminous  bowl  is 
a  deep  yellow  in  color  most  persons  will  unconsciously  associate 
this  color  with  the  useful  light  even  if  most  of  the  latter  arrives 
indirectly  at  the  point  of  interest  practically  unaltered  by  re- 
flections from  neutral  walls  and  ceiling.  The  resultant  light 
is  a  mixture  of  the  unaltered  indirect  component  and  the  com- 
paratively small  direct  compound  of  deep  yellow  light.  In 
order  to  illustrate  this  point  more  fully,  let  us  take  the  reverse 
case  where  the  bowl  is  a  white  opal  glass  and  the  ceilings  and 
walls  are  decorated  a  moderately  saturated  yellow.  Now  the 
resultant  light  may  be  of  the  same  color  as  in  the  previous  case, 
but  it  is  a  mixture  of  a  yellow  indirect  component  due  to  selec- 
tive reflection  from  the  surroundings  and  an  unaltered  direct 
component.  However,  many  persons  would  proclaim  the 
lighting  to  be  garish  white  or  cold,  because  in  the  impression 
made  upon  them,  the  color  of  the  lighting  unit,  if  it  is  in  a  con- 
spicuous position,  is  a  prominent  factor.  It  is  interesting  to 
note  the  part  that  illusion  plays  in  lighting;  in  fact,  it  is  easy 
to  conclude  that  in  illusions  some  of  the  greatest  possibilities 
in  lighting  are  found. 

The  psychological  effects  of  the  surroundings  are  very  im- 
portant in  many  aspects  of  lighting  and  may  be  taken  advantage 
of  in  solving  some  problems.  Some  excellent  examples  may  be 
drawn  from  experiences  with  artificial  daylight  and  ordinary 
artificial  light,  for  the  former  is  white  and  relatively  cold  as 
compared  with  the  yellowish  artificial  light.  Through  the 
persistence  of  habit,  nurtured  by  experience,  it  is  natural  to 
expect  an  artificial  illuminant,  especially  at  night,  to  be  of  a 
warm  tint.  This  has  led  some  to  express  their  displeasure  with 
the  psychological  effect  of  the  cold  artificial  daylight  despite 
its  superior  rendition  of  colors;  however,  the  surroundings 
may  be  utilized  effectively  in  swaying  the  impression.  Let  us 
take  the  show-window  where  the  portion  of  the  scene  occupied 
by  the  goods  on  display  is  a  small  part  of  the  total  scene. 
Artificial  daylight  from  concealed  units  will  illuminate  the  goods 
satisfactorily  though  the  coldness  of  the  scene  may  be  effectively 
reduced  or  neutralized  by  having  the  backgrounds  decorated 


THE  PSYCHO-PHYSIOLOCY  OF  COLOR  79 

or  draped  in  warm  colors.  Where  the  artificial-daylight  units 
are  used  at  night  it  is  inadvisable  to  have  the  surroundings  in 
cold  colors.  Another  example  is  that  of  illuminating  paintings 
on  a  wall.  An  illuminant  of  daylight  quality  is  nearly  always 
highly  desirable  for  such  purposes  but  there  has  been  an  objec- 
tion due  to  its  apparent  coldness  at  night.  It  is  gratifying  to 
note  that  museums  are  abandoning  this  prejudice  and  that 
proper  lighting  is  becoming  a  primary  consideration.  If  warm 
gray  surroundings  are  provided  for  the  paintings,  the  coldness 
of  the  setting  largely  disappears.  The  gilded  frame  is  also  a 
factor  in  adding  warmth  to  the  setting. 

The  foregoing  illustrates  that  decoration  is  intimately  inter- 
woven with  lighting  in  the  broader  sense.  If  we  are  to  employ 
light  to  the  limit  of  its  possibilities  in  lighting  effects,  the  tex- 
ture and  the  distribution  of  brightness  and  color  of  the  sur- 
roundings must  be  considered.  The  mood  or  impression  of  an 
interior  may  be  modified  by  varying  the  distribution  and  color 
of  the  light  even  if  the  decorations  remain  fixed;  however,  this 
is  a  handicap  in  lighting  which  could  be  removed  by  consider- 
ing lighting  and  decoration  jointly.  At  this  point  the  harmony 
and  esthetics  of  color  enter  the  lighting  problem  very  promi- 
nently but  it  is  beyond  the  scope  of  this  volume  to  discuss  these 
intimately.  They  are  touched  upon  occasionally  in  other  chap- 
ters but  in  closing  it  is  well  to  note  that  there  are  two  broad 
classes  of  color-harmonies;  namely,  those  of  sequence  in  hue, 
and  those  of  contrast.  In  " painting  with  light"  the  former, 
which  approaches  the  monochrome,  has  its  value  but  perhaps 
a  note  of  light  contrasting  in  color  with  the  color  of  the  more 
general  light,  is  a  most  pleasurable  simple  expedient  because 
the  beauty  of  the  delicate  tints  of  the  dominant  light  are  brought 
to  life  by  this  vital  spark. 


CHAPTER  X 
SIMULATING  THE  SPECTRUM  OF  DAYLIGHT 

An  artificial  illuminant  of  the  spectral  character  of  daylight 
is  desired  for  several  reasons.  Owing  to  the  comparative  uni- 
formity in  the  amounts  of  energy  distributed  throughout  the 
visible  spectrum  of  daylight,  this  illuminant  is  the  most  gener- 
ally acceptable  for  the  illumination  of  colored  objects.  Most 
of  the  artificial  illuminants  are  poverty-stricken  in  the  blue  end 
of  the  spectrum  and  some  of  them  are  still  less  suitable  for  the 
illumination  of  colored  objects  owing  to  gaps  in  their  spectra. 
The  foregoing  might  be  advanced  as  a  scientific  reason  for  the 
superiority  of  daylight  for  the  purpose  in  mind  but  a  more 
practical  reason  is  that  color-technology  has  developed  under 
daylight  and  mankind  has  learned  to  base  its  judgment  of 
colors  upon  their  daylight  appearances.  Owing  to  the  differ- 
ent appearance  of  colors  under  ordinary  artificial  light,  uncer- 
tainty and  confusion  arise  in  the  judgment  of  colors  and  accu- 
rate color-work  is  generally  impossible.  Under  modern  con- 
ditions many  activities  are  pursued  after  nightfall.  In  those 
cases  where  colored  objects  are  exhibited  and  color-work  is 
done — and  they  represent  a  larger  class  than  commonly  sup- 
posed— an  illuminant  of  daylight  quality  is  much  to  be  desired. 

Besides  these  reasons  there  are  faults  to  be  found  with  natural 
daylight  on  the  basis  of  momentary  fluctuations  in  intensity 
and  in  spectral  character.  Furthermore,  it  changes  in  quality 
from  season  to  season  owing  to  the  change  in  the  selective  re- 
flection of  natural  outdoor  surroundings  such  as  vegetation. 
In  crowded  cities,  daylight  is  altered  considerably  by  reflection 
from  painted  buildings,  brick  walls,  etc.,  so  that,  owing  to  all 
these  influences  daylight  is  far  from  being  constant.  Outdoors 
there  are  two  fairly  constant  qualities  of  daylight  on  a  clear 
day,  namely,  north  skylight  and  noon  sunlight.  Owing  to  the 
shifting  clouds  and  their  variations  in  density  these  qualities  of 

80 


SIMULATING  THE  SPECTRUM  OF  DAYLIGHT    81 

daylight  are  rarely  constant  for  any  period.  Even  at  an  eleva- 
tion high  above  the  earth  and  buildings,  the  effect  of  selective 
reflection  from  the  surface  of  the  earth  is  noticeable  for  the  chlo- 
rophyl  bands,  characteristic  of  the  light  reflected  by  green  vege- 
tation, have  been  detected  in  the  integral  daylight,  although 
these  are  absent  in  the  daylight  at  sea  as  has  been  found  by 
measurement.  In  consideration  of  all  of  these  influences  it  is 
evident  that,  for  very  accurate  color- work,  an  artificial  daylight 
is  desirable  even  in  the  daytime  because  such  an  illuminant  has 
the  advantage  of  being  constant  in  intensity,  distribution,  and 
quality.  Incidentally  the  distribution  of  light  is  not  unim- 
portant in  its  influence  on  the  appearance  of  colors. 

In  simulating  the  spectrum  of  daylight  it  is  necessary  to  de- 
cide which  quality  of  daylight  should  be  reproduced.  Noon 
sunlight  is  more  nearly  white  than  skylight  although  it  has  not 
been  standardized  as  white.  North  skylight  has  been  much 
favored  for  color-work  but  from  various  discussions  with  expert 
colorists  in  various  fields  it  is  concluded  that  its  choice  has  been 
due  largely  because  it  is  the  most  constant  of  all  the  daylights. 
If  clear  sunlight  were  depended  upon  there  would  be  many 
disappointments  because  for  many  days  in  succession  the  sun 
is  obscured  and  it  cannot  be  depended  upon  even  throughout 
a  given  day.  Measurements  show  that  the  variations  in  the 
intensity  of  north  skylight  (on  this  hemisphere)  are  very  much 
less  than  that  of  the  skylight  from  any  other  direction.  When 
the  sky  is  overcast  the  resultant  light  is  a  mixture  of  blue  sky- 
light and  direct  sunlight.  Sometimes  the  resultant  light  on  an 
overcast  day  is  quite  purplish  in  hue  but  the  variations  in  the 
quality  of  north  skylight  are  not  sufficient  to  be  extremely 
troublesome. 

There  appear  to  be  fields  for  both  artificial  noon  sunlight  and 
artificial  north  skylight  of  the  spectral  characters  shown  in  Fig. 
7.  The  former  is  to  meet  the  demand  for  white  light  of  a  prac- 
ticable luminous  efficiency  for  general  lighting  and  the  other 
to  provide  an  illuminant  which  more  nearly  approaches  the 
daylight  usually  encountered  indoors  and  which  is  a  close  match 
to  the  kind  of  daylight  more  generally  in  use  by  colorists. 
There  are  three  possible  methods  of  obtaining  artificial  day- 


82  THE  LIGHTING  ART 

light,  namely:  (i)  directly  from  an  artificial  light-source;  (2) 
by  combining  two  or  more  illuminants;  and  (3)  by  altering  an 
illuminant  in  spectral  character  by  the  use  of  selective  or  colored 
filters. 

The  Moore  carbon-dioxide  tube  emits  a  line  and  banded 
spectrum  which  approaches  closely  to  a  spectral  character 
between  that  of  sunlight  and  blue  skylight.  It  may  be  said 
to  simulate  very  closely  the  combined  light  from  the  sun  and 
blue  sky  or  the  light  on  a  thinly  overcast  day.  This  illuminant 
is  in  use  for  accurate  color- work. 

The  " snow- white"  flame  arc  emits  a  spectrum  filled  with 
closely  crowded  lines  which,  it  is  claimed,  approximates  the 
spectrum  of  combined  sunlight  and  skylight.  One  of  the  re- 
quirements of  accurate  color-work  is  steady  illumination  but 
the  flicker  of  the  arc  may  be  largely  overcome  by  the  use  of  two 
or  more  arcs  operating  simultaneously. 

Some  of  the  new, gas  mantles  are  said  to  approach  daylight 
in  spectral  character  but  no  analytical  data  are  available  to  the 
author. 

A  few  years  ago  a  mercury-vapor  arc  was  combined  with  a 
tungsten  lamp,  which  was  termed  an  orthochromatic  lamp,  the 
tungsten  lamp  supplying  the  red  rays  which  are  practically 
absent  in  the  light  from  the  mercury  arc.  This  combination 
gave  a  subjective  white  light  which  was  an  improvement  over 
either  illuminant  alone  but  which  could  not  be  used  for  general 
color-work  of  an  accurate  nature  owing  to  the  excessive  energy 
of  a  few  wave-lengths  representing  the  mercury  spectrum. 

For  cases  of  emergency,  and  perhaps  for  special  purposes, 
colored  lamps  of  a  hue  complementary  to  a  commercial  illumi- 
nant may  be  combined  with  the  latter  to  make  white  light. 
A  number  of  instances  are  on  record  where  blue-green  tungsten 
lamps  were  combined  with  clear  tungsten  lamps  to  provide  a 
white  light  for  the  illumination  of  colored  objects.  This  may  be 
done  very  easily  for  a  temporary  purpose  by  the  use  of  colored 
lacquers  properly  mixed  to  obtain  the  blue-green  comple- 
mentary to  the  yellowish  light  from  the  tungsten  lamp.  A 
considerable  correction  of  tungsten  light  can  be  made  toward 
daylight  by  coloring  the  inner  surface  of  a  reflector  possessing 


SIMULATING  THE  SPECTRUM  OF  DAYLIGHT       83 

a  rough  surface  such  as  exhibited  by  aluminized  surfaces. 
The  reflected  light  is  altered  to  a  blue-green  color  by  selective 
reflection  and  this  light  when  added  to  the  unaltered  cone  of 
direct  light  results  in  an  integral  light  which  is  materially  cor- 
rected toward  daylight.  An  impractical  feature  from  the  view- 
point of  obtaining  a  standard  quality  of  light  is  that  the  amount 
of  correction  depends  upon  the  portion  of  the  light  flux  which 
is  intercepted.  For  this  reason  various  reflectors  would  give 
different  results. 

The  most  extensive  applications  of  artificial  daylight  have 
been  through  the  use  of  specially  developed  glasses,  greenish- 
blue  in  color,  which  have  been  used  both  for  bulbs  of  tungsten- 
filament  lamps  and  for  accessories  in  the  form  of  plates  and 
blown  glassware.  The  advent  of  the  gas-filled  tungsten  lamps 
made  this  method  of  producing  artificial  daylight  practicable 
on  a  large  scale  although  the  scheme  has  also  been  applied  to  gas- 
mantle  units  with  success.  Artificial  noon  sunlight  is  produced 
with  gas-filled  tungsten  lamps  operating  at  about  16  lumens 
per  watt  with  a  loss  of  about  50  per  cent,  in  luminous  efficiency, 
and  artificial  north  skylight  at  a  loss  of  about  80  or  85  per  cent, 
in  luminous  output.  However,  luminous  efficiency  is  scarcely 
considered  in  the  case  of  the  artificial  skylight  units  because 
of  the  necessity  for  them.  Before  such  units  were  available 
a  great  deal  was  said  regarding  the  luminous  efficiency  but  it 
is  found  that  this  point  is  seldom 'mentioned  by  those  whose 
output  or  convenience  is  concerned.  It  is  impracticable,  li 
not  impossible,  to  produce  a  colored-glass  filter  which  alters  an 
illuminant  to  an  exact  reproduction  of  a  specific  daylight  quality 
so  that  the  final  proof  of  acceptability  is  found  in  actual  practice. 
For  this  reason  spectral  analyses  are  of  little  value  in  compari- 
sons but  must  form  the  basis  for  the  development  of  such  filters. 
The  chief  point  to  note  is  that,  for  example,  an  illuminant  may 
appear  white  but  unless  examined  spectrally  none  but  an  expert 
may  be  able  without  considerable  experimenting  to  judge 
whether  or  not  it  approaches  sufficiently  close  in  quality  to  that 
of  the  daylight  which  it  is  supposed  to  simulate. 

The  noon  sunlight  units  find  applications  in  the  rougher 
classes  of  color-work  such  as  lithographing,  commercial  art, 


84  THE  LIGHTING  ART 

etc.,  and  may  vary  further  from  the  ideal  than  the  skylight 
units  because  the  discrimination  of  color  is  not  very  exacting. 
There  is  a  vast  field  of  commercial,  industrial,  and  office  light- 
ing where  cost  must  be  considered  and  for  this  reason  another 
daylight  unit  has  appeared.  It  represents  a  compromise  be- 
tween quality  and  cost  of  light  and  is  a  gas-filled  tungsten  lamp 
equipped  with  a  blue-green  bulb,  being  known  commercially 
as  the  Mazda  C-2  lamp.  The  light  from  this  lamp  approaches 
sunlight  in  quality  and  its  luminous  efficiency  is  about  65 
per  cent,  of  the  same  lamp  equipped  with  a  clear  bulb.  The 
color  of  the  light  is  a  warm  daylight  and  is  especially  adaptable 
to  many  lighting  problems.  The  quality  of  the  light  approaches 
that  which  would  result  if  the  tungsten  filament  of  a  clear  lamp 
could  be  operated  at  a  temperature  hundreds  of  degrees  above 
its  present  melting  point. 

The  developments  along  this  line  have  been  chiefly  to  imitate 
daylight  and  thus  the  question  of  white  light  has  not  entered. 
The  problem  has  been  to  meet  the  demands  of  practice  rather 
than  to  reproduce  in  quality  an  ideal  regarding  which  there  is 
no  agreement.  There  have  been  offered  on  the  market  a 
number  of  so-called  "daylight"  units  which  have  had  little  merit 
but  these  have  not  withstood  the  test  of  practice.  The  eye 
alone  cannot  always  be  accepted  as  a  judge  of  the  approxima- 
tion to  daylight  which  has  been  attained  but  notwithstanding 
the  necessity  for  spectral  analyses  of  these  illuminants  the 
final  product  is  a  compromise  between  the  contemplated  ideal 
and  practical  considerations. 

A  few  years  ago  before  the  commercial  exploitation  of  many 
artificial-daylight  units  there  was  much  speculation  as  to  the 
requirements  but  the  final  tests  are  those  of  actual  practice. 
We  are  now  able  to  draw  conclusions  from  many  installations 
of  various  types  of  units  and  these  are  presented  in  the  next 
chapter. 


CHAPTER  XI 
APPLICATIONS  OF  ARTIFICIAL  DAYLIGHT 

Artificial  daylight  is  now  available  from  various  types  of 
lighting  units  and  as  a  commercial  illuminant  it  is  a  rapidly 
growing  factor  in  lighting  practice.  A  few  years  ago  when 
discussions  of  artificial  daylight  were  centered  about  theoretical 
and  impracticable  units,  the  supposed  field  for  such  units  was 
usually  limited  to  stores  and  to  textile  industries.  Since  the 
development  and  commercial  exploitation  of  units  more  gener- 
ally adaptable,  the  field  has  enlarged  far  beyond  the  limits 
set  by  those  experienced  in  the  illumination  requirements  of 
various  activities.  Owing  to  this  expansion  and  to  the  con- 
tinued recession  of  the  horizon  of  artificial  daylight  it  appears 
of  interest  to  discuss  many  of  these  applications  briefly.  In 
considering  future  applications  of  artificial  daylight  it  is  well 
to  note  that  even  when  natural  daylight  is  available  it  cannot 
be  brought  into  interiors  without  cost.  The  construction  of 
the  daylight  entrances  is  more  expensive  than  ordinary  roofing 
and  blank  walls.  In  crowded  cities  the  space  sacrificed  for 
light-courts  and  windows  reduces  the  possible  income  from  a 
given  area  of  ground.  Furthermore,  the  increased  cost  of 
heating  buildings  containing  large  areas  of  glass  is  not  an  in- 
appreciable item.  With  the  decreasing  cost  of  artificial  light 
it  is  conceivable  that  the  future  may  witness  a  keener  competi- 
tion between  artificial  and  natural  lighting. 

For  the  sake  of  brevity  in  expression,  all  units  will  be  pre- 
sented under  two  classes,  namely,  skylight  and  sunlight  units. 
The  Moore  tube  is  in  use  in  some  fields  for  accurate  color-match- 
ing. This  emits  an  excellent  quality  of  light  for  this  work. 
The  " snow- white"  flame  arc  has  found  some  application  for 
accurately  discriminating  colors  and  gas-mantle  units  provided 
with  colored  filters  are  in  use  to  some  extent.  Illuminating 
glassware  of  proper  spectral  characteristics  is  available  for  use 

85 


86  THE  LIGHTING  ART 

with  various  units,  chiefly  the  gas  and  incandescent  filament 
lamps.  Besides  these  there  are  available  at  present,  gas-filled 
tungsten  lamps  equipped  with  blue-green  bulbs  which  have  been 
more  generally  installed  than  other  units.  This  lamp,  known 
commercially  as  the  Mazda  C-2  lamp,  emits  a  light  of  a  qual- 
ity approximating  sunlight,  and  owing  to  its  relatively  high 
efficiency  and  adaptibility  it  has  been  extensively  applied. 

Many  factors  such  as  luminous  efficiency,  cost  of  lighting, 
natural  prejudices,  and  the  degree  of  approximation  to  natural 
daylight,  have  influenced  the  development  and  adoption  of 
artificial-daylight  lamps  and  accessories.  For  accurate  color- 
work  most  of  these  factors  vanish  and  the  skylight  units  are 
chosen.  For  this  field  there  are  available  the  Moore  tube,  the 
" snow- white"  flame  arc,  and  gas  and  electric  units  employing 
an  accurately  correcting  filter.  But  even  in  this  field  difficulties 
arise  because  the  colorist  has  been  accustomed  to  a  specific 
daylight  quality  peculiar  to  his  location.  It  is  impracticable 
to  provide  artificial  daylight  of  many  different  qualities  to  suit 
the  vagaries  of  daylight  (and  of  colorists)  but  if  an  artificial 
daylight  has  been  developed  properly  it  is  fair  to  submit  it  as  a 
substitute  for  natural  daylight  not  only  on  the  basis  of  its  spec- 
tral character  but  on  account  of  its  constancy  in  distribution, 
intensity,  and  quality.  Fortunately  the  need  for  such  units  is 
so  urgent  that  petty  prejudices  are  easily  swept  aside. 

But  there  is  a  great  field  for  artificial  sunlight  units  where  the 
esthetic  taste  is  a  prominent  factor.  Habit  has  decreed  that 
an  artificial  illuminant  for  many  places  should  be  yellowish 
instead  of  white.  In  such  cases  all  the  skill  of  the  lighting 
specialist  in  employing  the  psychological  effects  of  the  environ- 
ment is  necessary  in  order  to  provide  the  quality  of  light  needed 
without  offending  the  esthetic  sense.  The  sunlight  units  are 
more  adaptable  to  these  cases  besides  providing  a  satisfactory 
quality  of  light.  Perhaps  the  greatest  difficulty  encountered 
lies  in  convincing  the  consumer  that  he  should  take  the  long 
step  from  the  warm  artificial  light  to  the  cold  artificial  daylight. 
In  this  connection  it  is  well  to  avoid  installing  a  few  artificial- 
daylight  units  for  general  lighting  in  the  midst  of  a  number  of 
ordinary  yellowish  units  because  not  only  will  the  quality  of  the 


APPLICATIONS  OF  ARTIFICIAL  DAYLIGHT         87 

light  suffer  by  admixture  with  the  uncorrected  light  but  the 
daylight  units  will  appear  bluish  by  contrast  with  the  units 
which  contain  the  yellowish  illuminants.  Installations  should 
be  completely  changed  over  in  order  to  avoid  the  effects  of 
contrast.  The  apparent  coldness  of  artificial  daylight  in  stores 
is  not  often  noticed  by  the  customer  if  the  light  is  quite  well 
diffused  throughout  the  store  for  the  impression  which  the 
lighting  makes  upon  a  person  who  is  unfamiliar  with  the  instal- 
lation is  that  the  store  is  exceptionally  well-illuminated  by 
means  of  natural  daylight.  This  is  an  important  fact  which 
has  been  brought  out  in  many  cases. 

The  chief  points  can  be  discussed  best  by  means  of  actual 
cases  so  an  attempt  has  been  made  to  record  some  of  the  more 
important  fields  which  artificial  daylight  units  have  already 
invaded. 

Stores. — Among  these  are  included  tailor  shops,  dry  goods, 
clothing,  millinery,  and  furniture  stores  as  well  as  many  others. 
In  most  of  these  cases  skylight  units  are  desirable  at  the  coun- 
ters or  in  special  locations  for  accurate  color-matching.  These 
save  the  time  required  by  both  the  clerk  and  the  customer  to 
walk  to  a  window  or  doorway  which  is  commonly  done. 
Throughout  the  store  general-lighting  with  sunlight  units  is 
satisfactory.  Perhaps  the  most  annoying  condition  in  stores 
is  the  conflict  of  yellow  artificial  light  coming  predominantly 
from  units  overhead  with  the  bluish  skylight  arriving  nearly 
horizontally  from  distant  windows.  The  ceiling  should  be 
fairly  neutral  in  color  in  order  to  avoid  the  alteration  of  the 
indirect  component  by  selective  reflection  especially  where  this 
component  is  relatively  large  as  in  the  cases  of  indirect  and 
direct-indirect  lighting. 

Little  objection  to  the  coldness  of  the  artificial  daylight  is 
encountered  in  stores  which  are  well  supplied  with  natural 
daylight  because  the  artificial  and  natural  daylights  blend  so 
well  but  where  this  objection  is  encountered,  the  lighting  special- 
ist has  recourse  to  suggestions  regarding  the  decorative  scheme. 
This  objection  rarely  comes  from  the  customer.  Touches  of 
gilt  or  warm  shades  on  the  columns,  and  sparingly  on  the  walls 
and  ceiling,  work  wonders  in  relieving  this  impression.  Inci- 


88  THE  LIGHTING  ART 

dentally  it  is  convenient  and  desirable  to  have  two  small  con- 
necting rooms  lighted  respectively  by  ordinary  artificial  light 
and  artificial  daylight  where  the  customers  may  discriminate 
the  colors  under  either  illuminant.  This  applies  particularly  to 
the  sale  of  gowns,  rugs,  furniture,  millinery,  etc.,  which  require 
daylight  illumination  for  proper  inspection. 

Show-windows. — Artificial-sunlight  tungsten  lamps  have 
been  installed  quite  extensively  in  show-windows.  There  ap- 
pears to  be  no  better  place  for  them  for  the  functions  of  a 
window  are  to  attract  attention  and  to  display  goods.  The 
problem  is  relatively  simple  because  the  units  ordinarily  should 
be  concealed.  The  light  is  directed  upon  the  goods  and  the 
warmth  of  the  setting  may  be  retained  by  warm  tones  in  the 
background  and  draperies.  Not  only  are  textile  goods  dis- 
played well  under  artificial  daylight  but  many  other  commodi- 
ties. In  some  localities,  automobile  display  rooms  have  been 
equipped  largely  with  sunlight  units.  The  deep  shades  of 
color  commonly  employed  for  painting  automobiles  are  often 
undetectable  under  ordinary  artificial  light. 

Art  Galleries. — No  interiors  have  a  stronger  claim  for  the 
necessity  of  light  of  a  daylight  quality.  The  great  value  of 
works  of  art  should  arise  from  their  appearance  and  in  justice 
to  the  artist  (and  to  the  public)  his  product  should  be  exhibited 
under  light  approximating  daylight  in  spectral  character.  The 
sunlight  units  are  more  satisfactory  for  lighting  works  of  art 
and  a  number  of  galleries  have  been  lighted  by  artificial 
daylight. 

Microscopy. — The  importance  of  the  quality  of  light  in  mi- 
croscopy is  well  known.  Observations  which  are  continued 
after  nightfall  are  made  usually  with  more  certainty  under 
artificial  daylight.  The  natural  colors  of  minute  objects  are 
not  only  important  but  the  technology  of  staining  is  equally 
dependent  upon  the  discrimination  of  color.  Both  types  of 
units  are  in  use  in  microscopy  depending  usually  upon  the 
individual  requirements. 

Cigar  Factories. — Cigars  are  sorted  in  respect  to  color  and 
the  varieties  of  shades  of  brown  are  distinguished  with  difficulty 
if  at  all  under  yellowish  artificial  light.  Both  the  skylight  and 


APPLICATIONS  OF  ARTIFICIAL  DAYLIGHT         89 

the  sunlight  units  are  in  use  and  there  appears  to  be  little  dif- 
ference in  the  results  obtained  with  these  units  in  the  discrimi- 
nation of  the  various  browns  displayed  by  tobacco. 

Color  Factories. — Skylight  units  are  in  use  for  more  accurate 
color-discrimination  and  color-matching  and  sunlight  units  are 
employed  for  general  illumination  of  processes  less  exacting  in 
the  requirements  of  color-perception.  The  products  of  such 
factories  when  exhibited  in  stores  or  used  in  paint  shops  are 
also  at  present  illuminated  in  many  cases  by  means  of  daylight 
units. 

Paint  Shops. — Skylight  units  for  accurate  color-mixing  and 
for  the  standardization  of  colors  are  employed  in  considerable 
numbers  but  in  general  in  this  field  the  sunlight  units  are  used. 
The  final  product  is  well-displayed  under  such  illumination  and 
as  a  consequence  many  automobile  display  rooms,  for  example, 
are  illuminated  by  the  sunlight  units. 

Textile  Mills. — In  dye-mixing  and  testing,  skylight  units 
are  in  use.  Rows  of  such  units  are  also  used  parallel  to  the 
perches  upon  which  the  dyed  materials  are  hung.  An  angle 
unit  is  found  necessary  in  some  cases  in  order  to  illuminate  the 
material  which  hangs  vertically  and  is  inspected  by  the  light 
transmitted  as  well  as  by  that  which  is  reflected  by  the  material. 
In  accurate  dyeing  even  the  most  experienced  colorist  who  is 
thoroughly  familiar  with  the  spectral  characteristics  of  his 
dyes  is  often  unable  to  be  sure  of  his  ground  without  an  illu- 
minant  of  daylight  quality.  The  sunlight  units  or  those  emit- 
ting light  approximating  sunlight  in  quality  have  found  many 
applications  in  various  textile  mills.  The  same  difficulties  in 
discriminating  the  colors  of  textiles  persist  in  the  wholesale 
and  retail  stores,  so  that  many  of  these  establishments  have 
been  equipped  with  various  types  of  artificial  daylight  units. 

Garment  Factories. — Both  types  of  artificial  daylight  have 
been  applied  to  those  industries,  including  woolen  mills  and 
cotton  mills. 

Cotton  Exchanges. — Although  the  discrimination  of  different 
qualities  of  cotton  is  included  in  the  foregoing  classification  this 
activity  deserves  special  mention.  Raw  cotton  is  sorted 
into  a  vast  variety  of  grades  in  which  color  is  an  important 


90  THE  LIGHTING  ART 

factor.  The  colors  vary  from  a  white  to  a  yellowish-white, 
and  the  tints  are  so  weak  in  hue  that  it  is  quite  impossible  to 
discriminate  many  of  them  from  each  other  under  ordinary  yel- 
lowish artificial  light.  The  skylight  units  are  employed  for 
this  work. 

Furs. — All  the  difficulties  of  the  discrimination  of  color  are 
met  in  the  fur  industries.  Not  only  do  the  lighter  tints  present 
difficulties  under  ordinary  artificial  light  but  also  the  dark 
shades  which  are  so  commonly  encountered  in  furs.  Both 
classes  of  artificial-daylight  units  not  only  are  in  use  in  the 
industrial  activities  but  have  been  installed  by  wholesale  and 
retail  furriers. 

Color-printing. — In  mixing  inks  and  in  inspecting  proof, 
skylight  units  are  employed  and  for  the  presses  the  sunlight 
units  find  wide  application.  An  interesting  feature  of  artificial 
daylight  in  color-printing,  besides  the  satisfactory  rendition  of 
the  blues,  violets,  and  purples,  is  the  resulting  contrast  of 
yellows  upon  white  backgrounds  under  this  quality  of  light. 
Under  ordinary  artificial  light  it  is  difficult  to  distinguish  the 
yellow  impression  on  white  paper  in  three-color  printing. 
Pressmen  find  difficulty  in  distinguishing  flaws  under  such 
conditions  which  sometimes  results  in  considerable  spoilage. 
In  lithography,  art  work  on  the  original  drawing  and  the  work 
on  stones  is  now  being  favorably  done  under  artificial-daylight 
illuminants.  Wall-paper  displays  are  well  illuminated  by  the 
sunlight  units,  hence  the  latter  have  found  their  way  into 
wholesale  and  retail  wall-paper  stores. 

Art  Studios. — Installations  of  artificial  daylight  have  been 
made  in  studios  of  pure  and  applied  art.  Oddly  enough, 
artificial  daylight  of  a  sunlight  quality  is  often  preferred  not- 
withstanding the  general  choice  of  natural  north-skylight  for 
such  studios.  This  seeming  contradiction  is  likely  to  lead  one 
astray  if  further  inquiry  is  not  made.  North  exposure  has 
been  chosen  in  general  by  artists  not  chiefly  for  the  sake  of  the 
quality  or  color  of  the  light  but  because  north-skylight  is  the 
most  constant  natural  daylight  both  in  intensity  and  quality 
or  spectral  composition.  Some  discerning  artists  prefer  to 
paint  from  models  in  the  warmer  light  in  order  to  have  their 


APPLICATIONS  OF  ARTIFICIAL  DAYLIGHT         91 

paintings  tend  toward  the  warmer  tone.  For  example,  a 
model  appears  warmer  in  general  tone  under  a  warmer  light 
and,  therefore,  the  artist  will  paint  in  a  warmer  tone.  In 
fact,  one  of  our  greatest  artists  proposed  to  illuminate  the  model 
with  artificial  sunlight  and  his  canvas  with  artificial  skylight 
in  order  to  insure  the  warmth  of  tone  which  he  desired.  In- 
cidentally the  output  of  art  studios  is  materially  reduced  during 
winter  which  is  usually  a  busy  season.  It  is  significant  to  note 
the  acceptance  of  artificial  daylight  by  artists. 

Metal  Work. — The  discrimination  of  the  various  colors  of 
such  alloys  as  brass  and  commercial  gold  is  very  difficult  under 
ordinary  yellowish  artificial  light  because  the  various  mixtures 
appear  nearly  if  not  exactly  the  same  in  color.  Under  artificial 
daylight  the  differences  in  the  various  yellows  of  the  foregoing 
examples  are  readily  distinguishable  from  each  other.  Diffi- 
culties arise  with  other  metals  and  alloys  in  which  color-dis- 
crimination is  of  considerable  importance.  The  sunlight  units 
are  usually  satisfactory  in  these  cases.  Lacquering  activities 
are  often  more  satisfactorily  prosecuted  under  light  of  daylight 
quality. 

Ore  Refineries. — Color  plays  an  important  part  in  the  selec- 
tion and  judgment  of  ores  and  of  ore  concentrates  and  as  a 
consequence  this  field  has  been  invaded  by  artificial-daylight 
units.  A  bluish-gray  ore  appears  gray  under  yellowish  artifi- 
cial light  and  a  yellowish  ore  cannot  be  distinguished  easily  if  at 
all  from  another  specimen  of  a  gray  or  yellowish  tint.  In  the 
former  case,  the  specimen  is  found  to  be  a  bluish-gray  under 
artificial  daylight  and  in  the  latter  case  the  yellows  are  easily 
distinguished.  A  case  encountered  in  practice  is  the  presence 
of  yellowish  pyrites  in  lead  or  zinc  concentrates. 

Chemical  Analyses. — In  such  work  color-discrimination  is 
often  of  importance.  The  requirements  vary  so  that  either 
the  skylight  or  sunlight  units  are  satisfactory  depending  upon 
the  case.  In  titrating,  the  skylight  units  appear  to  be  more 
satisfactory.  The  concentration  of  a  weak  solution  is  some- 
times estimated  by  the  color  of  a  considerable  depth  of  the 
solution.  An  example  of  this  is  the  yellowish  color  of  chlorine 
solutions.  When  of  low  concentration  this  yellowish  tint  can 


92  THE  LIGHTING  ART 

be  distinguished  with  difficulty  if  at  all  under  ordinary  artificial 
light. 

Laundries. — Dirt,  spots  due  to  scorching,  and  other  blem- 
ishes which  are  generally  yellowish  in  hue  are  more  readily 
distinguishable  under  artificial  daylight  than  under  ordinary 
artificial  light.  "  Bluing, "  which  is  used  to  neutralize  the 
yellowish  hue  of  white  fabrics,  can  be  applied  with  more  cer- 
tainty under  artificial  daylight.  The.  sunlight  units  are  usu- 
ally satisfactory  in  laundries. 

Paper  Mills. — In  the  manufacture  of  paper  the  problems 
of  distinguishing  delicate  tints  of  approximately  white  papers 
and  of  tinting  pulp  to  match  certain  standards  are  commonly 
met.  Artificial  daylight  has  met  these  problems  satisfactorily. 

Flour  Mills. — In  a  similar  manner  artificial  daylight  units  are 
in  use  for  distinguishing  the  delicate  tints  of  flour. 

Sugar  Refineries. — Skylight  units  are  in  use  for  distinguishing 
the  colors  of  sugars. 

Jewels. — Color  is  an  important  factor  in  the  value  of  jewels 
and  the  illuminant  influences  the  colors  of  jewels  quite  markedly. 
Diamonds  present  special  difficulties  because  commercial 
diamonds  vary  in  color  from  blue- white  to  a  decidedly  yellow- 
ish tint.  The  former  lose  their  bluish  tinge  and  the  latter  ap- 
pear less  yellow  under  ordinary  artificial  light.  The  skylight 
illuminants  are  usually  desired  for  purposes  of  examination  of 
jewels.  Pearls  and  opals  often  lose  some  of  their  beauty  under 
ordinary  artificial  light  owing  to  the  suppression  of  the  blues 
and  violets  and  to  the  shifting  of  the  pinks  toward  red. 

Dentistry. — Matching  artificial  teeth,  cements,  porcelain 
inlays,  etc.,  present  difficulties  both  in  factories  and  in  the  den- 
tal offices.  Skylight  units  are  in  use  for  the  more  exacting  work 
but  the  sunlight  units  are  found  quite  satisfactory  for  much  of 
the  work. 

Woodwork. — Under  yellowish  artificial  light  it  is  difficult  to 
distinguish  the  colors  of  various  woods  and  the  variety  of  tints 
of  the  same  wood  because  these  are  ordinarily  of  a  yellowish  or 
reddish  hue.  In  furniture  manufacture  it  is  often  necessary 
to  match  wood  with  care  and  it  has  been  found  that  artificial 
sunlight  is  a  desirable  illuminant  for  such  work. 


APPLICATIONS  OF  ARTIFICIAL  DAYLIGHT         93 

Medicine  and  Surgery. — Artificial  daylight  has  found  its 
way  into  hospitals  and  private  offices  for  use  in  surgical  opera- 
tions and  in  diagnosis.  Various  types  of  units  are  in  use  de- 
pending upon  the  requirements  and  upon  the  desires  of  the 
users.  It  is  difficult  to  distinguish  the  various  colors  of  healthy 
and  diseased  tissues  and  manifestations  of  skin  diseases  are 
sometimes  unrevealed  or  difficult  to  observe  under  yellowish 
artificial  light. 

The  foregoing  are  a  few  of  the  activities  in  which  artificial 
daylight  is  in  use.  These  are  sufficient  to  bring  forth  the  rami- 
fications of  the  problem  of  discriminating  color  in  industrial 
and  commercial  activities;  however,  there  are  many  more  ap- 
plications on  record.  The  following  are  some  of  the  additional 
places  and  activities  in  which  artificial  daylight  is  in  use  at 
the  present  time:  barber  shops,  hairdressing,  haberdasheries, 
button  factories,  green  houses,  shoe  stores,  libraries,  under- 
taking, chiropody,  dry-cleaning,  displays  of  colored  photo- 
graphs and  of  ordinary  photographic  negatives,  breweries  and 
upholstering. 

Many  unique  and  unexpected  applications  have  been  met  in 
practice  and  it  appears  that  the  field  for  such  lighting  units 
will  be  greatly  extended.  Instances  have  been  found  in  which 
users  have  declared  that  a  light  of  a  daylight  quality  is  easier 
on  the  eyes  for  close  work  than  yellowish  light.  In  the  absence 
of  a  decisive  method  of  testing  this  point  such  statements  must 
be  given  some  attention,  especially  inasmuch  as  it  is  a  reason- 
able possibility  when  viewed  from  the  standpoint  of  evolution 
and  adaptation.  One  of  the  most  prominent  features  is  the 
miscibility  of  artificial  daylight  with  natural  daylight.  There 
appears  to  be  an  unsatisfactory  condition  of  lighting  when 
natural  daylight  must  be  reinforced  with  yellowish  artificial 
light.  As  a  result  of  this  many  installations  of  artificial  day- 
light have  been  made  in  offices,  drafting  rooms,  etc.,  where  the 
discrimination  of  the  colors  of  objects  is  of  little  or  no  impor- 
tance. In  many  of  these  applications  esthetic  taste  is  a  second- 
ary consideration .  Where  this  is  a  primary  factor  the  resourceful 
lighting  specialist  may  be  able  to  solve  the  problem  satisfac- 
torily. There  are  many  ways  of  using  artificial  daylight  which 
satisfy  the  esthetic  sense. 


CHAPTER  XII 

SPECIAL  APPLICATIONS  OF  COLORED 
LIGHT 

There  are  many  special  uses  for  illuminants  of  certain  spectral 
compositions  some  of  which  will  be  described  not  only  for  them- 
selves but  to  give  the  reader  a  broader  view  of  the  importance 
of  the  spectral  character  of  the  illuminant.  Through  intimate 
acquaintance  with  the  spectral  characteristics  of  illuminants 
and  of  niters  and  with  the  lighting  requirements  of  many 
activities,  the  lighting  specialist  may  greatly  extend  his  use- 
fulness beyond  the  boundaries  more  generally  recognized. 

In  the  field  of  photography  the  lighting  specialist  has  a  num- 
ber of  avenues  open  to  him  whereby  he  may  be  of  service. 
Artificial  lighting  in  the  portrait,  commercial,  and  moving- 
picture  photographic  studios  is  becoming  an  important  factor 
owing  to  its  constancy,  adaptability,  and  general  reliability. 
The  most  common  illuminants  in  use  for  making  photographic 
negatives  are  the  mercury  arcs,  the  various  carbon  arcs,  and 
the  gas-filled  tungsten  lamps  among  which  the  special  blue- 
bulb  (Mazda  €-3)  photographic  lamp  is  the  most  practicable. 
The  problem  of  distributing  the  light  in  the  most  efficient  man- 
ner is  clearly  one  for  which  the  illuminating  engineer  is  especi- 
ally trained  and  the  problem  of  obtaining  the  proper  lighting 
effects  is  one  for  the  lighting  artist.  Observation  in  this  field 
has  led  to  the  conclusion  that  the  specialist  in  lighting  can  do 
much  in  coordinating  science  and  art  in  photographic  studios. 
The  problem  is  chiefly  one  of  devising  easy  controls  for  ob- 
taining a  flood  of  light  and  dominant  light  of  various  degrees  of 
directedness.  Combinations  of  these  two  extremes  provide  a 
vast  variety  of  artistic  effects. 

There  are  many  factors  involved  in  the  choice  of  photographic 
illuminants  which  are  so  interrelated  and  differently  evaluated 
depending  upon  the  conditions  or  effect  which  is  desired,  that 

94 


SPECIAL  APPLICATIONS  OF  COLORED  LIGHT       95 

it  is  impossible  to  establish  a  common  basis  for  comparison. 
Actinic  or  photographic  value  is  the  first  requirement  and  in 
most  cases  adaptability  or  ease  of  control  of  the  distribution 
of  light,  is  doubtless  the  factor  next  in  importance.  In  the 
latter,  the  portability  of  the  lighting  units  is  often  of  impor- 
tance. Investigation  has  shown  that  generally  the  cost  of 
energy  is  much  less  significant  than  the  two  factors  mentioned 
above  owing  to  the  relatively  small  portion  of  time  in  which  the 
lighting  units  are  in  operation  in  the  photographic  studio. 
Furthermore,  it  is  obvious  that  the  economics  of  the  problem 
must  not  be  based  upon  the  facts  of  ordinary  lighting  but  upon 
the  facts  of  "  photographic  "  lighting. 

In  the  photographic  dark-room  several  colored  illuminants 
are  necessary  depending  upon  the  photographic  emulsions  in- 
volved. It  is  well  known  that  most  ordinary  emulsions  are 
sensitive  chiefly  to  ultra-violet,  violet,  blue,  and  blue-green  rays 
and  practically  insensitive  to  yellow,  orange,  and  red  rays. 
For  this  reason  red  light  is  quite  commonly  used  for  the  illu- 
mination of  dark-rooms  for  the  purpose  of  manipulating  ordi- 
nary plates.  The  red  should  preferably  be  without  an  orange 
hue  and  should  appear  a  very  deep  red.  This  may  be  obtained 
by  the  use  of  red  glass  or  red  lacquers  although  it  is  not 
uncommon  to  find  that  the  latter  often  transmit  violet  light 
appreciably.  By  adding  a  yellow  lacquer  this  fault  may  be 
remedied.  For  handling  printing  paper  which  is  much  less 
sensitive  as  a  rule  than  ordinary  plates  and  films,  an  orange- 
red  or  even  yellow  light  is  quite  satisfactory. 

Panchromatic  emulsions  are  sensitive  to  all  the  rays  of  the 
visible  spectrum  and  also  to  ultra-violet  rays.  However,  the 
sensitivity  of  such  emulsions  is  by  no  means  the  same  for 
energy  of  all  wave-lengths  and  a  relatively  low  sensitivity  is 
often  found  in  the  green  region  between  0.5/4  and  0.55^.  This 
is  near  the  spectral  region  of  maximum  luminosity  of  radiation 
at  low  intensities ;  therefore  a  low  intensity  of  illumination  from 
a  fairly  monochromatic  illuminant  having  a  maximum  of 
luminosity  near  0.50  to  0.52^  (green  light)  is  found  satisfactory 
for  handling  panchromatic  emulsions.  It  would  be  quite  out 
of  place  to  discuss  the  illumination  requirements  of  photog- 


96  THE  LIGHTING  ART 

raphy  in  detail  but  a  few  have  been  touched  upon  in  order  to 
bring  this  field  to  the  attention  of  the  lighting  specialist.  There 
are  many  other  requirements  met  by  various  illuminants;  for 
example,  the  arcs  are  in  use  for  blueprinting  and  photo-engrav- 
ing and  many  tungsten  lamps  of  all  sizes  are  in  use  for  printing. 
Gas  lamps  are  in  use  to  some  extent  in  photographic  studios. 

In  signalling,  the  ranges  and  visibilities  of  colored  lights  are 
important  factors.  It  has  been  found  that  for  a  given  illumi- 
nant  the  range  increases  approximately  directly  with  the  candle- 
power  when  the  absorption  of  the  atmosphere  is  negligible.  To 
what  extent  the  color  of  the  illuminant  affects  the  range  or 
visibility  of  a  signal  light  is  not  accurately  determined  but  it 
is  found  to  be  quite  an  influence  under  practical  conditions  of 
atmospheric  absorption.  It  has  been  shown  that  fine  particles 
of  water-vapor,  dust,  smoke,  ice  and  perhaps  the  molecules  of 
air  scatter  the  violet  and  blue  rays  more  than  the  other  visible 
rays.  For  this  reason  an  illuminant  in  which  yellow,  orange,  and 
red  rays  predominate  should  penetrate  farther  under  ordinary 
atmospheric  conditions  than  one  rich  in  energy  of  the  shorter 
wave-lengths.  This  is  especially  noticeable  by  the  reddish 
color  of  the  setting  sun  which  indicates  that  the  energy  of  short 
wave-lengths  in  the  visible  spectrum  have  suffered  greater 
absorption  or  scattering  than  the  longer  wave-lengths.  The 
scattered  light  should  therefore  be  of  a  bluish  color  similar  to 
skylight  which  apparently  is  scattered  sunlight.  This  fact 
has  led  to  the  development  of  search-light  and  automobile 
headlamps  equipped  with  yellow  screens.  It  is  not  only  claimed 
that  by  eliminating  the  violet  and  blue  rays  there  is  less  scatter- 
ing in  dust  and  fog  but  that  there  is  less  glare  from  the  yellow 
light.  The  latter  point  is  quite  in  doubt  at  present  but  there 
appears  to  be  a  possibility  of  a  slight  advantage  in  yellow 
screens  from  the  viewpoint  of  the  observer  behind  the  lamp 
owing  to  the  reduction  of  the  "  veiling"  glare  due  to  the  scat- 
tered light;  however,  this  point  requires  more  definite  proof. 

One  of  the  most  important  factors  which  influence  the  choice 
of  colored  illuminants  for  signalling  purposes  is  the  brightness 
or  intensity  obtainable  under  practical  conditions.  It  is  well 
known  that  ordinary  illuminants  contain  relatively  small 


SPECIAL  APPLICATIONS  OF  COLORED  LIGHT        97 

amounts  of  violet  and  blue  rays  and  for  this  reason,  purple 
and  blue  are  essentially  short-range  signals.  Yellow  is  the  most 
luminous  but  red  is  more  striking  and  practically  unmistakable. 
Fortunately  it  possesses  the  desirable  characteristics  of  fair 
luminosity,  relatively  slight  alteration  in  intensity  and  in 
color  by  atmospheric  absorption,  and  striking  appearance. 
Blue-green  is  usually  of  fair  luminosity  and  green  and  orange 
are  other  possible  signal  colors.  Signal  lenses  have  other 
practical  uses  in  lighting  especially  as  screens  for  obtaining 
fairly  pure  colored  illuminants. 

It  is  obvious  that  a  danger  signal  may  possibly  come  to  be 
ignored  if  it  burns  steadily  at  all  times ;  therefore  it  appears  that 
a  haphazard  flicker  in  intensity  from  a  certain  moderately  low 
value  to  a  high  one  would  be  desirable.  At  no  time  should  the 
brightness  become  zero  or  even  so  low  as  to  be  unnoticeable 
but  certainly  there  would  be  some  value  in  a  superposed,  spas- 
modic flicker  for  attracting  attention. 

Some  time  ago  it  was  brought  to  the  author's  attention  that 
a  battleship  which  had  just  been  launched  was  equipped  with  a 
lighting  circuit  of  blue  lights  for  use  when  in  an  engagement  at 
night  or  at  least  when  near  the  enemy.  The  reason  for  using 
the  blue  lights  was  not  clear  but  doubtless  was  for  the  purpose 
of  obtaining  maximum  luminosity  with  sources  of  low  intensity. 
It  is  a  physiological  fact  of  vision  that  at  low  intensities  the 
wave-length  of  maximum  visibility  is  in  the  blue-green  region 
of  the  spectrum  in  the  neighborhood  of  o.5i/u.  This  is  a  fact 
that  might  well  be  borne  in  mind  in  selecting  phosphorescent 
materials  for  special  purposes. 

It  has  become  well  established  that  visual  acuity  or  the  ability 
to  discriminate  fine  detail  is  better  under  monochromatic  light 
than  under  an  illuminant  of  extended  spectral  character.  This 
fact  may  be  taken  advantage  of  in  special  cases.  Monochro- 
matic light  is  satisfactorily  used  for  microscopy  and  should 
have  other  applications.  Among  the  common  illuminants  the 
mercury  arc  approaches  monochromatism  more  closely  than 
any  other.  Most  of  the  luminosity  is  due  to  the  green  line 
(0.546;*)  and  the  twin  yellow  lines,  (0.577/4  and  0.579/1).  The 
maximum  visibility  of  radiation  of  ordinary  intensities  lies 


98  THE  LIGHTING  ART 

close  to  the  green  mercury  line  at  about  0.55^.  This  is  a  fact 
to  be  noted  in  special  cases  where  a  purely  monochromatic 
light  of  high  intensity  is  desired.  The  green  mercury  line  may 
be  isolated  by  suitable  screens  and  perhaps  is  the  best  mono- 
chromatic illuminant  available  for  visual  purposes.  It  is 
known  that  the  eye  ordinarily  focuses  blue  objects  with  diffi- 
culty except  at  close  range  so  that  such  factors  usually  must  be 
considered. 

The  author  has  made  experiments  on  the  effect  on  visual 
acuity  of  absorbing  from  a  continuous-spectrum  illuminant  the 
rays  near  the  ends  of  the  spectrum.  For  example,  by  the  use 
of  yellow  niters,  varying  in  saturation,  more  and  more  of  the 
blue  end  of  the  spectrum  of  tungsten  light  was  absorbed,  the 
resulting  light  varying  in  seven  steps  from  the  unaltered  yellow- 
ish tungsten  light  to  a  deep  amber.  Although  the  experiments 
were  not  thoroughly  conclusive  it  appeared  that  visual  acuity 
remained  practically  constant  notwithstanding  the  reduction 
in  the  illumination  due  to  the  yellow  filters.  It  appears  that 
there  are  possibilities  of  such  applications  to  special  problems 
in  future  lighting. 

Light  is  in  use  for  medicinal  purposes  but  little  is  known  along 
this  line  except  the  germicidal  action  of  light,  especially  of 
ultraviolet  rays.  The  psychologist  and  physiologist  must 
unearth  more  data  before  the  lighting  specialist  can  do  much 
more  in  this  field  than  to  carry  out  the  wishes  of  others.  How- 
ever, there  are  many  cases  in  which  the  lighting  specialist  may 
be  helpful  by  analyzing  the  spectra  of  illuminants  and  filters 
and  by  providing  colored  illuminants  as  well  as  by  properly 
equipping  ordinary  illuminants  for  medicinal  purposes. 

The  problem  of  simulating  the  color  of  older  illuminants  such 
as  the  candle  flame  is  a  scientific  one,  the  chief  aim  of  such  a 
realization  is  to  satisfy  the  requirements  of  esthetic  taste. 
There  is  no  doubt  that  the  warm  yellowish  tint  of  the  light  from 
the  candle  flame,  kerosene  flame,  and  carbon-filament  lamp  is 
very  pleasing  in  many  interiors;  however,  the  haphazard 
attempts  to  imitate  such  illuminants  by  means  of  colored  filters 
applied  to  modern  light-sources  fall  far  short  of  success.  The 
usual  procedure  has  been  to  take  a  yellow  coloring  element 


SPECIAL  APPLICATIONS  OF  COLORED  LIGHT        99 

and  incorporate  it  in  glass,  lacquer,  or  other  medium  but  this 
invariably  has  resulted  in  an  amber  color.  If  the  esthetic 
sense  is  so  finely  tuned  as  to  require  the  unsaturated  yellow 
illumiriants  it  is  certain  that  in  general  the  greenish-yellow, 
characteristic  of  light  tints  of  yellow  coloring  media,  will  not  be 
acceptable.  Amber  illuminants  border  on  the  spectacular 
whereas  the  inconspicuous  yellowish  tint  of  the  candle  flame 
is  an  artistic  color  which  blends  harmoniously  in  many  interiors. 
The  best  proof  of  the  foregoing  is  to  illuminate  two  diffusing 
glass  bowls  with  amber  and  "  candle-flame  "  illuminants  respec- 
tively. The  former  will  be  conspicuous  to  everyone  whereas 
the  latter  will  not  appear  " colorful"  though  the  " warmth"  of 
the  light  is  felt.  It  may  be  said  that  the  latter  color  is  felt  but 
not  seen. 

Silk  fabrics  are  more  readily  obtainable  of  the  proper  color 
than  other  colored  media.  Ordinary  yellow  glasses  or  lac- 
quers lose  their  greenish  tinge  by  the  addition  of  a  pink  and  the 
desired  yellow  may  be  thus  obtained.  By  mixing  the  light 
transmitted  by  a  very  deep  yellow-orange  glass  with  clear  tung- 
sten light  a  fair  result  may  be  obtained.  This  may  be  done  as 
in  Fig.  ii.  The  author  has  obtained  the  color  in  glass  with  a 
single  coloring  element  under  proper  conditions  and  also  in 
lacquers  and  in  other  superficial  coatings.  Such  developments 
are  certainties  of  the  future  in  order  to  convert  modern  illumi- 
nants into  those  warmer  tints  so  satisfactory  for  many  interiors. 

It  may  be  of  interest  to  learn  the  highest  efficiencies  at  which 
illuminants  of  the  spectral  characters  of  the  candle  flame  may 
be  obtained  by  applying  filters  to  the  tungsten  lamps  operating 
at  various  efficiencies.  These  are  presented  in  the  accompany- 
ing table  with  similar  values  of  efficiency  for  simulating  the 
spectrum  of  the  carbon-filament  lamp  (3.1  m.p.c.)  Obviously 
light  of  the  quality  of  that  emitted  by  the  carbon  lamp  can 
be  obtained  at  a  higher  luminous  efficiency  from  the  tung- 
sten lamp  equipped  with  a  proper  filter  than  from  the  carbon 
lamp  itself.  These  values  were  computed  and  represent  accurate 
spectral  matches.  Under  the  less  rigid  requirements  of  practice 
somewhat  higher  luminous  efficiencies  of  the  filtered  light  may 
be  expected.  In  the  first  column  the  normal  operating  effi- 
ciencies is  given  for  clear  lamps. 


100  .  THE  LIGHTING  ART 

SIMULATING   OLD   ILLUMINANTS  BY   FILTERING   TUNGSTEN   FILAMENT  LIGHT 


Lumens  per  watt 

Filtered  to  simulate 

T            t        fi1              t  1 

Candle  flame 

Carbon,  filament 

(Vacuum  type) 

6.c 

3-9 

TI 

5-3  ' 

8.0 

4-5 

6-3 

10.  0 

S-o 

7-i 

12.0 

5-6 

8.0 

14.0 

6.0 

8.9 

(Gas-filled) 

8.0 

S-i 

7-4 

IO.O 

5-7 

8-4 

12.0 

6-3 

9-3 

14.0 

6-9 

IO.2 

16.0 

7-4 

II.  0 

18.0 

8.0 

ii.  6 

20.  o 

8-5 

12.  2 

22.  O 

9.0 

12.7 

Colored  glasses  have  been  used  for  modifying  daylight  before 
it  enters  interiors.  A  yellowish  tint  somewhat  similar  to  that 
required  for  converting  tungsten  light  to  a  color  approximating 
that  of  the  candle  flame  alters  blue  skylight  to  the  color  of  sun- 
light. A  glass  of  such  a  color  should  find  many  applications  in 
buildings  and  it  is  not  beyond  the  bounds  of  possibility  to  find 
such  glass  come  into  use  for  glazing  north  windows  in  office 
buildings.  The  north  skylight  is  cheerless  and  when  we  begin 
to  realize  the  psychological  effect  of  the  color  of  light,  the  finer 
points  of  lighting  will  be  given  closer  attention.  Incidentally 
there  appears  to  be  a  need  for  skylight  glass  which  is  fairly 
opaque  to  infra-red  rays.  Such  glass  would  rob  sunlight  of 
some  of  its  energy  and  therefore  aid  in  keeping  interiors  cool. 

The  possibilities  of  utilizing  light  of  various  colors  or  qualities 
are  numerous  and  represent  a  definite  line  of  development  in 
lighting.  The  foregoing  discussion  treats  a  few  of  these  not 
only  for  themselves  but  for  the  purpose  of  suggesting  the  scope 
of  this  relatively  untrodden  field. 


CHAPTER  XIII 
SIMPLE  PRINCIPLES  OF  LIGHT-CONTROL 

With  the  practical  development  of  the  possibilities  of  con- 
trolling the  distribution  and  quality  of  light,  the  lighting  spe- 
cialist finds  many  interesting  fields  outside  those  of  ordinary 
interior  and  exterior  illumination.  The  development  and  the 
installation  of  such  devices  as  projection  lanterns,  searchlights, 
headlights  and  lenses  as  well  as  ordinary  lighting  equipment 
are  often  left  to  him.  It  is  not  uncommon  to  be  confronted 
with  the  problems  involving  both  the  quality  and  the  distribu- 
tion of  light  for  photography  and  even  for  medicinal  and  vari- 
ous hygienic  purposes.  As  the  lighting  specialist  becomes 
qualified  he  finds  that  he  is  called  upon  to  supply  illuminants 
for  dye  and  paint  testing,  for  bleaching  purposes,  and  at  least 
to  render  opinions  in  many  other  fields.  There  are  many  ap- 
plications of  colored  light  especially  in  relation  to  chemical 
and  physiological  phenomena.  It  is  quite  beyond  the  scope 
of  this  volume  to  discuss  this  aspect  widely  but  a  glimpse  of 
various  phases  and  specific  applications  will  be  presented. 

Control  of  the  distribution  of  light  is  obtained  by  reflection 
and  by  refraction.     There  are  many  kinds  of  surfaces  available 
for  lighting  purposes  which  are  used  to  control  light  by  reflec- 
tion but  among  the  transparent  or  translucent  substances, 
glass  is  the  most  commonly  used.     However,  glass  is  a  name 
which  applies  to  a  large  variety  of  compounds  or  mixtures  vary- 
ing considerably  in  their  optical  characteristics.     Perhaps  no 
better  idea  of  the  control  of  light  or  of  the  appearance  of  object 
due  to  the  light  reflected  and  refracted  by  them  can  be  obtaine 
than  by  a  few  simple  illustrations. 

In  a,  Fig.  12,  /  represents  an  incident  beam  of  light  upon  a 
mirrored  or  optically  plane  surface,  and  R  the  reflected  beam. 
It  is  a  simple  law  of  optics  that  the  angle  of  incidence  is  equal 
to  the  angle  of  reflection  for  a  beam  of  light  incident  upon  an 

101 


102  ttiE.  LIGHTING  ART 


optically  plane  surface.  In  practice,  the  so-called  mirrors 
such  as  polished  metals  and  other  materials,  chemically  depos- 
ited metals,  varnished  surfaces,  and  various  glazes  reflect  light 
regularly  as  indicated  in  a,  Fig.  12.  It  is  evident  that  excellent 
control  of  light  is  possible  by  the  use  of  mirrored  surfaces  of 
contours. 

There  are  many  surfaces  which  diffuse  the  incident  light, 
almost  perfectly  as  indicated  by  b,  Fig.  12.  It  is  seen  that  the 
beam  incident  upon  the  diffusely  reflecting  surface  is  scattered 
in  all  directions.  "Flat"  paints,  blotting  paper,  dry  pigments 
and  plaster  as  well  as  many  other  surfaces  are  diffusely 
reflecting  but  perhaps  no  surface  is  perfectly  so. 


A--» 


b 

FIG.  12. — Common  reflection  characteristics. 


Another  type  of  reflection  is  illustrated  in  c,  Fig.  12.  This 
"spread"  reflection  is  exhibited  by  sand-blasted  and  aluminized 
surfaces,  depolished  brass,  and  others.  It  will  be  noted  that 
the  light  is  maximally  reflected  at  an  angle  of  reflection  corre- 
sponding to  the  angle  of  incidence  although  the  reflected  beam 
is  somewhat  scattered.  If  the  beam  of  light  is  incident  per- 
pendicularly to  the  surface  the  latter  will  reflect  relatively 
more  light  perpendicularly  if  it  has  a  reflecting  characteristic 
like  that  shown  in  c,  Fig.  12,  than  if  it  is  perfectly  diffusing  as 
shown  in  b,  Fig.  12.  Although  this  fact  is  of  chief  interest  in 
lighting  from  the  viewpoint  of  the  design  of  reflectors,  it  is 
exceedingly  pertinent  to  the  moving-picture  screen.  In 
theatres  whose  width  is  small  compared  with  the  length,  a 
screen  of  the  spread-reflection  type  has  advantages  but  in  com- 
paratively wide  theatres  a  diffusely  reflecting  screen  is  neces- 
sary in  order  that  the  pictures  will  be  bright  enough  when 
viewed  by  those  seated  near  the  sides  of  the  room  or  at  con- 


SIMPLE  PRINCIPLES  OF  LIGHT-CONTROL         103 

siderable  distances  from  the  center-line  connecting  the  pro- 
jection lantern  and  the  screen. 

The  maximum  reflection-factors  of  such  surfaces  as  indicated 
in  Fig.  12  are  not  greatly  different  in  value.  Under  excellent 
conditions  0.9  is  about  the  highest  value  maintainable  in  prac- 
tice for  either  the  regularly  reflecting  mirror  or  the  diffusely 
reflecting  white  surface.  Many  combinations  of  these  char- 
acteristics are  encountered  in  practice;  for  example,  a  white 
enamel  surface  or  a  sheet  of  blotting  paper  covered  with  thin 
glass  gives  a  combination  of  the  types  illustrated  in  a  and  b, 
Fig.  12. 

With  translucent  or  transparent  substances,  the  phenomenon 
of  refraction  is  present.  This  may  be  best  illustrated  by  a 


J  £  c 

FIG.  13. — Common  characteristics  of  transmitting  media. 

few  cases.  In  a,  Fig.  13,  a  beam  of  light  /  is  shown  incident 
upon  a  transparent  surface  of  S.  A  portion  of  the  light,  R,  is 
shown  reflected  regularly  from  the  polished  or  glazed  surface 
but  the  remaining  portion  T  is  transmitted  though  in  another 
direction.  The  fact  that  the  direction  of  T  is  different  than 
/  indicates  that  the  refractive  index  of  S  is  different  than 
that  of  the  medium  through  which  /  passes.  For  a  given  angle 
of  incidence  the  portion  of  the  incident  light  which  is  reflected 
by  the  surface  depends  upon  the  refractive  indices  of  the  two 
media.  If  5  is  ordinary  glass  surrounded  by  air,  the  portion 
of  the  reflected  light  is  about  4  per  cent,  for  each  surface  if  the 
beam  of  light  is  incident  perpendicularly  to  the  surface.  This 
proportion  increases  with  the  angle  of  incidence,  slowly  at  first 
then  more  rapidly  and  obviously  no  light  enters  S  when  the 
incident  angle  becomes  equal  to  90  degrees.  The  relation 
between  the  reflection-factor  for  an  ordinary  thin  sheet  of 


104 


THE  LIGHTING  ART 


clear  glass  and  the  angle  of  incidence  is  shown  in  Fig.  14.  The 
lower  curve  is  for  the  first  surface  with  the  beam  of  light  incident 
from  air  and  the  upper  curve  is  for  the  two  surfaces.  The 
index  of  refraction  of  the  glass  is  1.52.  The  transmission- 
factors  may  be  determined  in  any  case  by  subtracting  the  re- 
flection-factor from  unity,  assuming  no  absorption  in  the  glass. 


1.00 


0.90 


0       10       20      30     40      50     60     70      60 

ANGLE    OF  INCIDENCE  (DEGREES) 

FIG.  14. — Relation  of  reflection-factor  and  angle  of  incidence  of  light  on  a 
thin  polished  plate  of  glass  having  a  refractive  index  of  1.52.  Upper  curve  for 
two  surfaces;  lower  curve  for  one  surface. 

If  the  substance  is  highly  diffusing  and  possesses  a  polished 
surface,  the  result  is  as  indicated  in  b,  Fig.  13.  Some  of  the 
light  which  is  diffusely  scattered  in  the  medium  S  finds  its  way 
back  into  the  air  but  this  is  not  shown  in  the  diagram.  If  the 
surface  is  sand-blasted,  c  represents  the  optical  characteristic. 
In  practice,  two  polished  surfaces  are  often  encountered  close 
together  as  in  the  case  of  thin  clear  glass.  The  most  im- 
portant reflected  and  transmitted  rays  are  shown  in  the  full 
lines  in  Fig.  15.  A  portion  of  the  incident  light  would  be 
accounted  for  in  R\,  somewhat  less  in  Rz  and  practically  the 
remainder  in  the  transmitted  beam  T  which  has  been  refracted 


SIMPLE  PRINCIPLES  OF  LIGHT  CONTROL         105 

at  each  surface.  If  the  two  surfaces  are  parallel  T  proceeds 
in  the  same  general  direction  as  /  but  slightly  displaced. 
As  a  matter  of  fact  if  a  certain  portion  of  the  total  incident 
light  is  reflected  at  each  " air-glass"  or  " glass-air"  surface,  it 
is  obvious  that  there  are  many  other  reflected  and  transmitted 
beams  as  indicated  by  the  dotted  lines.  These  become  negli- 
gible because  they  contain  but  a  small  portion  of  the  original 
incident  light.  If  the  second  surface  of  the  thin  glass  is  silvered 
the  intensity  of  R%  will  be  high.  This  accounts  for  the  double 
reflected  image  seen  in  plate  glass  and  mirrored  glass. 


FIG.  15. — A  thin  plate  of  polished  glass. 

Reflection  is  a  factor  in  all  reflectors  whether  opaque,  trans- 
parent or  translucent.  It  appears  unnecessary  to  illustrate 
how  ordinary  lighting  units  of  different  types  of  distribution 
are  obtained  because  this  field  is  one  for  the  specialist  in  de- 
signing. His  tools  are  optical  laws,  characteristics  of  the  sur- 
faces and  media  at  his  disposal,  and  the  distribution  curves  of 
light-sources.  However,  it  should  be  of  interest  to  illustrate 
a  few  of  the  applications  of  optical  principles  in  the  control  of 
light  which  are  useful  to  the  lighting  specialist  in  solving  certain 
problems.  Many  of  these  are  based  on  the  assumption  of  a 
point  source  of  light  which  is  never  realized  in  practice.  For 
this  reason  certain  compromises  are  made  in  design  and  often 
certain  difficulties  arise  which  cannot  be  readily  overcome. 

The  focus  of  a  spherical  mirror  is  at  the  center  of  curvature; 
that  is,  at  the  center  of  the  spherical  envelope.  If  a  point 
source  which  emits  light  of  equal  intensities  in  all  directions, 
a,  Fig.  1 6,  be  placed  at  the  center  of  curvature  of  a  spherical 


106 


THE  LIGHTING  ART 


mirror  of  180  degrees  solid-angle  as  shown  in  b,  Fig.  16,  the 
intensity  in  the  various  directions  away  from  the  mirror  will 
be  increased.  If  the  silvered  spherical  surface  is  perfectly 


y 


FIG.  1 6. — The  spherical  mirror. 

reflecting  the  intensity  in  any  direction  away  from  the  mirror 
is  doubled.  This  condition  is  not  realized  in  practice  but  the 
spherical  mirror  may  be  used  to  advantage  to  approach  such 


i k 


^ 


FIG.   17. — The  parabolic  mirror. 

a  result.  If  the  spherical  surface  is  diffusely  reflecting,  the 
maximum  intensity  will  lie  on  the  axis  but  the  distribution  of 
the  light  from  the  unit  will  differ  very  much  from  that  shown 
in  b.  Furthermore,  the  output  will  be  less  than  in  the  case 


SIMPLE  PRINCIPLES  OF  LIGHT  CONTROL         107 

of  the  mirrored  surface  even  with  the  same  reflection-factors 
of  the  mirrored  and  diffusing  surfaces  owing  to  the  greater 
absorption  due  to  internal  multiple  reflections  (and  therefore 
absorptions)  in  the  case  of  the  diffusing  surface. 

The  law  of  the  parabolic  mirror  has  been  utilized  in  such 
units  as  searchlights,  headlamps,  and  flood-lighting  units.  If 
a  point  source  be  placed  at  the  focus  of  such  a  mirror,  the  rays 
intercepted  by  the  reflector  are  rendered  parallel  as  indicated 
by  the  full  lines  in  a,  Fig.  17.  There  is  always  a  cone  of  direct 
light  emitted  as  indicated  by  the  dotted  lines.  Although  there 
are  many  practical  considerations  which  limit  the  design  it  is 
evident  that  the  larger  the  solid-angle  of  intercepted  light,  the 
greater  is  the  percentage  of  the  total  light  which  is  rendered 


(b) 

FIG.   1 8. — The  parabolic  mirror. 


parallel.  The  shallow  parabolic  mirror  shown  in  b  emits  a 
greater  percentage  of  unintercepted  light  in  the  direct  cone 
than  the  relatively  deeper  unit  shown  in  a.  If  the  direct  cone 
of  light  is  not  desired,  it  may  be  eliminated  or  at  least  reduced 
in  importance,  by  means  of  circular  black  diaphragms  placed 
in  front  of  the  unit  and  perpendicular  to  the  axis  or  by  opaque 
cylinders  concentric  with  the  axis.  Such  simple  expedients 
are  useful  in  special  problems.  Inasmuch  as  light-sources  are 
not  confined  to  the  theoretical  point  there  is  a  certain  spread 
or  lack  of  perfect  control  in  nearly  all  commercial  units.  The 
automobile  headlamp  is  especially  important  and  it  is  interest- 
ing to  note  why  the  parallelism  is  not  obtained.  This  is 
shown  in  a,  Fig.  18,  where  the  light-source  is  shown  as  a  small 
sphere.  Small  cones  D  replace  the  theoretical  straight  lines 
in  the  preceding  illustrations.  If  the  light-source  is  in  front 


108 


THE  LIGHTING  ART 


of  the  focus  the  rays  cross  in  front  of  the  reflector  as  shown  in 
b.  By  placing  a  semicircular  shield  over  the  lamp  or  aperture 
to  cut  off  the  rays  emitted  by  the  lower  half,  the  remaining  light 
is  seen  to  be  directed  below  the  horizontal.  If  the  light-source 
is  behind  the  focus  the  rays  diverge  as  shown  in  c.  In  order 
to  eliminate  the  upward  light  it  is  necessary  to  obstruct  the 


FIG.   19. — The  elliptical  mirror. 

light  emitted  by  the  upper  half  of  the  unit.  These  are  simple 
expedients  which  have  been  applied  more  or  less  successfully 
to  automobile  headlamps. 

The  principle  of  the  elliptical  mirror  is  that  if  a  point  source 
of  light  is  placed  at  one  focus /i,  Fig.  19,  the  light-rays  will  be 


a  *> 

FIG.  20. — Refraction  of  a  prism  (a);  of  a  lens  (6). 

brought  to  a  point  again  at  the  other  focus /2.     These  illustrate 
some  of  the  principal  simple  laws  of  reflection. 

Some  of  the  possibilities  of  controlling  light  by  refraction  will 
be  illustrated  by  simple  examples.  If  a  beam  of  light  /  in  a, 
Fig.  20,  be  incident  upon  a  prism  of  glass  it" will  be  bent  from 
its  source  and  will  emerge  in  the  direction  of  R.  Under  the 
conditions  of  a  small  parallel  beam  the  emergent  ray  will  be 
spread  out  into  a  spectrum  owing  to  the  fact  that  the  refractive 


SIMPLE  PRINCIPLES  OF  LIGHT-CONTROL 


109 


index  of  the  glass  varies  with  the  wave  length  of  light.  This 
has  been  treated  in  another  chapter  and  inasmuch  as  the  condi- 
tion is  seldom  met  in  practice,  no  account  of  prismatic  dispersion 
will  be  taken  in  the  present  discussion. 

A  simple  lens  may  be  considered  to  be  described  by  a  prism 
rotated  about  its  base.  Thus  in  b,  Fig.  20,  the  focusing  effect  of 
a  simple  lens  is  illustrated.  Rays  of  all  wave-lengths  do  not 
come  to  a  focus  at  the  same  point  for  the  same  reason  that  they 
are  not  all  deviated  by  the  same  amount  by  a  prism.  This  is  a 
fault  of  all  simple  lenses  which  is  known  as  chromatic  aberra- 
tion. It  is  corrected  by  combining  with  a  simple  convex  lens 
a  glass  of  another  refractive  index.  For  information  on  com- 
binations of  lenses  the  reader  should  consult  a  book  on  optics. 


FIG.  21. — Lenses. 


If  in  the  case  of  a  simple  convex  lens,  the  light-source  is  placed 
at  a  distance  equal  to  the  focal  length  of  the  lens  the  rays  of 
light  are  rendered  parallel  on  emerging  as  shown  in  a,  Fig.  21. 
With  lenses  of  short  focal  length,  b,  the  cone  of  light,  u,  which 
is  utilized  is  greater  than  with  lenses  of  longer  focal  length,  a. 
A  spherical  silver  mirror  placed  behind  the  source  in  b  in  such 
a  position  that  its  center  of  curvature  is  coincident  with  the 
light-source,  will  increase  the  luminous  output  of  the  lens  in  the 
case  of  some  commercial  sources.  The  position  of  the  mirror 
and  the  cone  of  light  reflected  by  it  are  shown  by  the  dotted 
lines  in  b.  The  divergent  beam  from  a  concave  lens  is  shown  in 
c.  The  rays  of  light  appear  to  come  from  a  source  close  to  the 
lens  as  indicated  by  the  intersection  of  the  dotted  lines.  Total 
reflection  from  glass  surfaces  is  often  utilized  in  the  control 


110 


THE  LIGHTING  ART 


of  light,  for  example  as  shown  in  Fig.  22,  where  /  and  R  are 
respectively  the  incident  and  reflected  beams.  Light-rays  are 
totally  reflected  from  a  " glass-air"  surface  when  the  angle  of 
incidence  is  as  great  or  greater  than  the  angle  shown  provided 
they  are  passing  through  the  glass  medium  just  before  reaching 
the  surface  which  is  bounded  by  air. 


/  H 

b 


FIG.  22. — Total  reflection  in  glass. 


Prism  glass  is  used  in  many  ways  in  illuminating  engineering. 
There  is  a  vast  variety  of  designs  most  of  which  employ  the 
principle  of  bending  the  ray  through  an  appreciable  angle  by 
refraction  as  illustrated  in  Fig.  23.  In  employing  prism  glass 


FIG.  23. — Prism  glass. 

there  are  many  points  to  be  considered,  especially  the  character 
of  the  light-source;  that  is,  whether  it  be  of  small  solid-angle  or 
of  large  solid-angle  such  as  an  expanse  of  sky.  In  lighthouse 
lenses  and  other  signal  lenses  the  principle  of  refraction  is  suc- 
cessfully employed  in  controlling  light-rays  and  prismatic  illumi- 
nating glassware  has  been  used  extensively  for  many  years. 


SIMPLE  PRINCIPLES  OF  LIGHT-CONTROL          111 

In  summarizing  it  may  be  stated  that  the  principles  involved 
in  controlling  the  distribution  of  light  are  chiefly  those  of 
reflection  and  refraction.  Those  surfaces  or  translucent  media 
which  scatter  the  light  have  comparatively  narrow  limitations 


FIG.  24. — Control  of  light  by  devices  possessing  mirrored  surfaces. 


FIG.  25. — Control  of  light  by  prismatic  glass  devices. 

as  controlling  media  although  they  serve  the  requirements  of  a 
vast  amount  of  lighting  in  an  excellent  manner.  This  class  is 
represented  by  aluminized  and  enamelled  surfaces  and  by 
sand-blasted,  etched,  and  opal  glasses.  Polished  metals  and 


112  THE  LIGHTING  ART 

silvered  glasses  are  only  limited  in  their  ability  to  control  light 
by  such  practical  considerations  as  the  accuracy  with  which 
the  surfaces  can  be  made  to  approach  the  ideal  and  the  concen- 
tration and  brightness-uniformity  of  light-sources.  The  di- 
versity in  the  control  obtainable  by  mirrored  surfaces  is  repre- 
sented in  Fig.  24  as  well  as  in  some  of  the  preceding  illustrations. 

Similar  remarks  apply  to  the  utilization  of  reflection  and 
refraction  of  glass.  In  Fig.  25  are  shown  a  few  of  the  different 
distributions  of  light  obtainable  by  applying  these  principles 
in  the  design  of  so-called  prismatic  glassware.  Even  greater 
concentrations  may  be  obtained  by  means  of  prismatic  lenses 
and  combinations  of  simple  lenses  such  as  are  employed  in  op- 
tical instruments.  These  principles  are  the  tools  of  the  designer 
of  lighting  devices  and  are  available  to  the  lighting  specialist  in 
solving  his  problems. 

No  doubt  there  are  many  special  combinations  of  the  princi- 
ples of  reflection  and  refraction  which  will  be  adapted  to  the 
light-sources  and  to  requirements  of  the  future.  In  this  chap- 
ter merely  a  brief  glimpse  of  a  few  simple  principles  has  been 
given,  however,  these  few  principles  form  the  basis  of  light- 
control. 


CHAPTER  XIV 
LIGHTING  AND  ARCHITECTURE 

The  relation  between  lighting  and  architecture  is  of  interest 
from  several  important  viewpoints.  During  the  design  of  a 
building  a  general  idea  of  the  lighting  plan  should  be  determined 
so  that  the  necessary  provisions  may  be  made  during  the  con- 
struction. If  the  lighting  plans  are  not  fairly  well-defined  at 
this  time,  it  is  not  uncommon  for  the  lighting  specialist  to  be 
confronted  with  obstacles  which  could  have  been  avoided. 
Owing  to  this  lack  of  consideration  of  the  lighting  early  in  the 
design  of  a  building,  much  criticism  has  been  heaped  upon  archi- 
tects for  their  lack  of  cooperation  with  lighting  specialists. 
This  criticism  is  just  in  many  cases  but  there  is  another  view- 
point which  must  be  considered  in  justice  to  the  architect, 
namely  the  attitude  of  the  lighting  specialist  toward  his  prob- 
lems. In  the  case  of  a  beautiful  architectural  work  the  archi- 
tect maintains  in  his  imagination  the  final  picture  or  effect 
which  he  is  striving  to  realize.  In  this  final  result,  lighting  is 
only  one  of  the  factors — but  it  is  an  extremely  important  one. 
If  the  architect  consults  a  lighting  specialist  and  finds  that  the 
latter  attacks  the  problem  as  if  it  were  purely  an  engineering 
one  it  is  not  surprising  that  the  architect  is  disappointed. 
If  the  lighting  specialist  does  not  appreciate  that  the  architect 
is  striving  for  an  effect  and  is  not  designing  a  building  for  the 
purpose  merely  of  housing  a  lighting  system  which  is  to  provide 
an  illumination  of  a  certain  number  of  foot-candles  upon  a  given 
plane,  he  cannot  render  much  service  which  the  architect  can- 
not obtain  from  his  own  staff.  The  spacing  and  locating  of 
outlets  in  accordance  with  the  decorative  patterns  is  a  simple 
procedure  quite  obvious  to  many  outside  the  lighting  field. 
The  lighting  specialist  should  be  able  to  suggest  the  placing  of 
outlets,  the  types  of  units,  the  influence  of  the  decorative 
scheme,  the  effect  of  light  in  modelling  ornament,  and  the 

113 


114  THE  LIGHTING  ART 

general  psychological  and  artistic  effects  of  certain  distributions 
of  light,  shade  and  color  upon  different  details,  areas,  and  the 
interior  as  a  whole.  A  few  lighting  specialists  are  capable  of 
doing  this  but  there  is  much  progress  to  be  made  by  the  rank 
and  file  who  practice  illuminating  engineering. 

However,  the  architect  often  reveals  his  own  lack  of  apprecia- 
tion of  the  importance  and  potentiality  of  lighting  by  postponing 
the  consideration  of  lighting  until  the  building  is  well  under 
way.  He  has  solved  many  of  the  problems  of  daylighting 
because  these  must  be  considered  even  in  the  first  sketches 
but  the  possibilities  of  artificial  lighting  have  enormously 
extended  in  recent  years  so  that  he  has  not  yet  fully  appreciated 
their  full  value  and  importance.  Thus  it  is  seen  that  both  the 
architect  and  the  lighting  specialist  are  responsible  for  the 
much  discussed  lack  of  cooperation  between  them.  A  thorough 
treatment  of  the  subject  of  this  chapter  would  extend  into  a 
large  part  of  lighting  practice  so  that  only  a  general  introduc- 
tion will  be  presented.  The  relation  between  lighting  and 
architecture  crops  out  in  other  chapters  and  has  been  treated 
in  an  analytical  manner  elsewhere.1  There  are  certain  fields, 
such  as  industrial  and  office  lighting  in  which  the  purely  utili- 
tarian and  hygienic  aspects  are  of  chief  or  of  sole  importance. 
In  such  cases  the  illuminating  engineer  is  doing  excellent  work 
and  the  architect  may  find  plenty  of  expert  assistance  among 
these  engineers  in  solving  the  natural  and  artificial  lighting 
problems.  The  procedure  in  such  cases  is  largely  that  of 
illuminating  engineering,  the  practice  is  fairly  well  standardized, 
and  helpful  data  are  available.  However,  in  those  cases  where 
the  decorative  and  psychological  aspects  of  lighting  predominate, 
the  practice  is  not  standardized  and  perhaps  never  can  be. 
Individuality  is  a  characteristic  in  these  cases  and  a  procedure 
must  be  adopted  which  aims  to  produce  the  effect  desired.  The 
first  step  is  to  obtain  a  definite  idea  of  the  architect's  goal  and 
therefore  a  thorough  discussion  of  the  construction,  ornamental 
details,  decorative  scheme  and  other  factors  must  be  obtained 
by  consultation  and  from  specifications. 

First,  let  us  consider  the  effect  of  the  distribution  of  light 
*M.    LUCKIESH:    "Light    and    Shade    and    Their    Applications,"     1916. 


LIGHTING  AND  ARCHITECTURE  115 

upon  architectural  details  and  upon  the  artistic  and  psycho- 
logical aspects  of  an  interior  as  a  whole.  It  should  be  recog- 
nized that  lighting  models  objects  and  makes  areas  distinguish- 
able from  each  other.  These  light  and  shade  effects  aided 
by  the  colors  of  details  and  by  the  tints  and  shades  of  the  larger 
areas  are  responsible  for  whatever  artistic  or  psychological 
value  an  interior  may  possess.  But  the  architect  may  say 
that  this  is  not  true,  because  lines,  proportions,  etc.,  contribute 
something.  Indeed  they  contribute  to  the  final  effect  but 
only  through  the  agency  of  lighting. 

It  is  interesting  to  speculate  as  to  how  far  an  impression  of 
an  interior  is  gained  solely  through  that  which  is  seen  and  that 
which  is  not  seen  but  is  known  to  be  present.  For  example,  a 
vertical  panel  in  a  wall  may  be  surrounded  by  an  ornamental 
molding  mitered  at  the  four  corners.  Only  when  the  light  is 
distributed  upon  these  four  pieces  of  molding  from  a  point 
approximately  upon  a  line  perpendicular  to  the  center  of  the 
panel  will  they  appear  closely  alike.  Even  under  these  condi- 
tions they  will  .vary  somewhat  in  appearance  at  different  por- 
tions. If  the  dominant  light  arrives  from  a  source  higher  than 
the  panel  it  is  obvious  that,  in  the  general  case,  the  upper  mold- 
ing will  appear  quite  different  from  the  lower  one  which  presents 
a  different  side  toward  the  light-source.  Such  conditions  are 
to  be  found  in  nearly  all  decorative  interiors  yet  we  have  little 
fault  to  find;  however,  if  the  details  be  studied  carefully  the 
great  differences  in  the  appearances  of  the  same  molding-de- 
sign in  various  places  are  obvious.  This  leads  to  the  question, 
How  much  is  our  impression  of  an  interior  due  to  that  which  we 
gain  solely  through  vision?  Certainly  our  ability  to  reason  is 
an  influence  but  it  appears  that  lighting  should  be  more  care- 
fully prosecuted  with  the  appearances  of  details,  areas,  and 
the  whole  in  mind. 

A  similar  case  will  be  found  in  the  exhibition  of  paintings. 
For  example,  we  might  find  a  Corot  badly  lighted  by  means  of 
yellowish  artificial  light  and  under  the  conditions  it  may  not  be 
possible  to  view  it  to  advantage  or  to  distinguish  the  delicate 
bluish  grays.  It  is  interesting  to  note  the  expressions  of  delight 
on  the  part  of  those  who  discover  its  presence  though  most  of 


116  THE  LIGHTING  ART 

the  artistic  value  of  the  painting  is  unrevealed.  Such  effusions 
cause  the  searcher  after  knowledge  to  doubt  the  sincerity  in 
art-appreciation  of  many  individuals  posing  as  appreciators. 
Surely  the  pleasure  in  the  foregoing  example  is  not  due  to  that 
which  is  seen.  In  fine  art  of  this  character  there  appears  to 
be  much  pleasure  gained  from  possessing  the  object  or  from 
knowing  that  it  has  been  caressed  by  the  hand  of  antiquity 
or  is  a  product  of  the  same  hand  that  made  other  objects  of 
artistic  appeal. 

The  foregoing  is  of  importance  in  analyzing  the  part  that 
lighting  should  play  in  revealing  an  artistic  object,  whether 
the  latter  be  a  detail  or  a  whole  interior.  After  considerable 
experimentation,  observation  and  thought,  no  final  answer  to 
the  foregoing  question  has  been  reached  so  it  has  appeared 
necessary  to  cling  to  the  idea  that,  after  all,  the  artistic  or  psy- 
chological value  of  an  interior  lies  in  its  appearance  and  hence  is 
largely  a  matter  of  lighting.  The  distribution  of  light,  through 
the  values  of  light  and  shade  which  it  gives  to  the  dominant 
areas  and  through  its  modelling  of  details  combined  with  the 
color  effects,  produces  the  final  mood  or  spirit  of  the  interior. 
The  importance  of  this  statement  is  obvious  to  those  who 
experiment  with  lighting  effects  and  it  is  apparent  to  anyone 
who  takes  the  trouble  to  observe  lighting  effects  in  architectural 
interiors  such  as  churches  and  various  other  beautiful  interiors. 
A  striking  feature  of  the  study  of  lighting  is  that  studies  are 
to  be  found  on  every  hand. 

In  the  application  of  lighting  to  architecture  many  illusions 
will  be  observed.  A  dark  alcove  will  appear  darker  as  the 
brightness  of  the  surroundings  is  increased.  A  bright  ceil- 
ing may  produce  the  effect  of  the  airiness  of  outdoors  never- 
theless the  ceiling  is  seen  to  be  a  boundary  between  indoors 
and  outdoors.  A  dark  ceiling  may  appear  lofty  and  if  this 
darkness  is  enhanced  by  means  of  lighted  chandeliers  between 
the  eyes  and  the  dark  ceiling,  the  darkness  may  be  effective 
in  arousing  various  ideas  or  emotions  depending  upon  the  par- 
ticular setting.  Another  fact  of  lighting  and  vision  is  that  a 
bright  object  amid  dark  surroundings  usually  appears  larger 
than  when  the  light  and  shade  is  reversed.  In  Fig.  26  an 


LIGHTING  AND  ARCHITECTURE 


117 


attempt  has  been  made  to  illustrate  this  effect  and  to  relate  it 
to  architecture.  The  dimensions  are  exactly  the  same  in  the 
two  cases  but  the  dark  columns  appear  thinner  and  taller  than 
the  bright  ones.  Illusions  should  not  be  ignored  in  lighting. 

Various  alterations  may  be  made  in  the  architectural  pro- 
portions of  an  interior  by  the  proper  application  of  light  and 
shade.  The  decorator  knows  this  well  but  for  some  reason  light- 
ing has  not  been  considered  as  a  decorative  medium  in  the 
same  manner  as  pigments.  In  fact,  it  is  a  decorative  medium 
of  much  greater  expressive  possibilities  than  any  other  medium 


FIG.  26. — An  optical  illusion  of  light  and  shade. 

as  discussed  in  Chapter  II.     In  view  of  this  the  decorative  and 
lighting  schemes  should  be  considered  together. 

Fixtures  may  be  designed  and  located  so  as  to  produce  the 
best  effects  in  modelling  details  and  to  distribute  the  light  in  a 
manner  which  is  in  harmony  with  the  mood  to  be  realized. 
The  design  may  be  such  as  to  be  completely  in  accord  with  the 
artistic  scheme  or  period  style  of  the  interior  and  as  such,  the 
fixtures  may  be  beautiful  ornaments.  Their  locations  should 
be  considered  from  the  standpoint  of  eye-comfort  but  the 
proper  revealing  of  ornamental  details  is  also  of  importance. 
For  example,  if  the  walls  of  a  room  are  ornamented  by  means  of 
very  low  relief,  the  latter  will  be  seen  better  if  the  lighting  units 
are  placed  near  the  walls  above  the  relief  because  such  details 
are  revealed  in  the  best  manner  by  means  of  directed  oblique 
light.  Similarly,  if  a  ceiling  is  covered  with  low  relief,  it  is 
usually  unsatisfactory  to  flood  it  with  light  from  various  direc- 
tions. Such  lighting  tends  to  obliterate  low  relief.  In  some 
cases  the  light-sources  may  be  concealed  close  to  the  ceiling 


118 


THE  LIGHTING  ART 


behind  a  projecting  cornice  and,  as  shown  in  Fig.  27,  if  reflectors 
giving  an  asymmetrical  distribution  of  light  are  used,  a  satis- 
factory effect  may  be  obtained.  By  this  means  the  relief  is 
lighted  quite  obliquely  and  its  outlines  will  be  apparent  by 
lines  of  light  and  shade.  Incidentally  it  is  of  interest  to  note 
that  the  principle  of  low  relief  approaches  closely  to  that  of 
drawing  because  usually  the  expression  is  not  one  of  masses  of 
light  and  shade  but  chiefly  of  lines  of 
light  and  shade.  In  most  other  objects 
masses  are  prominent  factors. 

At  this  point  it  is  well  to  note  that  the 
appearances  of  objects  which  depend  upon 
shadows  and  highlights  are  influenced  by 
three  factors.     The  position  of  the  domi- 
nant light-source  determines  the  direction 
of  the  shadows;  the  solid-angle  subtended 
by  the  light-source  at  a  shadow-producing 
edge  determines  the  character  or  gradient 
of    the  modulation  of  brightness  in  the 
shadow-edge,     and    the    scattered    light 
and    that    arriving    from   distant   light- 
FIG.  27.— Cove-lighting,    sources  determine  the  brightness  of  the 
shadows .     These  factors  may  be  controlled 
to  a  degree  in  practice  and  thus  severity  or  softness  of  effect 
may  be  obtained  as  well  as  other  appearances. 

The  brightness  of  a  surface  depends  upon  its  reflection-factor 
(hence  upon  the  decorative  scheme)  and  upon  the  flux  density 
or  illumination  upon  the  surface.  Obviously  the  latter  depends 
upon  the  amount  of  light  directed  and  scattered  toward  the 
surface,  upon  the  orientation  of  the  surface,  upon  its  distance 
from  the  light-source  and  upon  various  details.  The  orienta- 
tion of  the  surface  is  highly  important  and  this  factor  should  be 
studied  in  respect  to  ornamental  patterns,  large  surfaces,  etc. 
For  example,  the  upper  part  of  a  wall — the  frieze — may  be 
brighter  than  the  portion  of  the  ceiling  adjacent  to  it  if  it  has 
the  same  reflection-factor,  because  the  light  is  received  by  this 
portion  of  the  wall  more  nearly  perpendicularly  than  by  the 
adjacent  portion  of  the  ceiling  from  a  light-source  at  some  dis- 


LIGHTING  AND  ARCHITECTURE  119 

tance.  This  is  especially  true  in  small  rooms  in  which  there  is  a 
central  fixture.  The  reverse  is  often  true  in  the  case  of  wall- 
brackets. 

If  a  light-source  is  suspended  from  the  center  of  an  architec- 
tural pattern  the  various  surfaces  of  the  latter  will  be  of  differ- 
ent brightnesses,  even  though  of  the  same  reflection-factor,  due 
to  their  different  orientations  with  respect  to  the  light-source. 
The  relation  of  lighting  to  architecture  is  found  to  involve  a 
vast  number  of  details  such  as  those  which  have  been  dis- 
cussed. The  full  import  will  not  be  grasped  until  much  study 
and  thought  have  been  applied  to  the  relation  of  lighting  to  the 
appearances  of  objects.  This  involves  the  scientific  aspects  of 
simple  optical  laws,  the  reflecting  characteristics  of  surfaces, 
the  distribution  and  color  of  light,  and  the  esthetic  and  psy- 
chological effects  of  distributions  of  light,  shade,  and  color. 

The  intensity  and  diffusion  of  daylight  in  architectural  in- 
teriors tends  to  alleviate  some  of  the  difficulties  which  arise 
from  lack  of  forethought  in  respect  to  the  influence  of  lighting 
upon  architecture  but  daylighting  usually  falls  short  of  the 
ideal  because  of  the  difficulty  in  controlling  its  distribution. 
With  the  advantage  of  controlling  artificial  light  both  in  dis- 
tribution and  in  color  it  is  far  superior  to  natural  light  in  the 
hands  of  a  lighting  specialist  who  recognizes  the  potentiality 
of  lighting  and  who  knows  how  to  utilize  it  scientifically,  artis- 
tically, and  psychologically.  In  fact,  it  appears  reasonable  to 
predict  that,  owing  to  the  superior  advantages  of  artificial  light 
in  these  respects,  it  will  not  be  unusual  to  find  places  where 
artificial  light  is  used  exclusively  even  though  daylight  were 
available  if  the  openings  had  been  provided 

The  foregoing  has  touched  upon  some  of  the  possibilities  of 
lighting  but  no  thought  is  entertained  that"  the  subject  has  been 
done  full  justice.  This  cannot  be  done  without  greatly  extend- 
ing the  discussion  but  the  aim  has  been  to  convince  those  in- 
terested in  lighting  that  they  wield  a  tool  of  extensive  possi- 
bilities in  relation  to  architecture.  Perhaps  a  few  examples  and 
suggestions  pertaining  to  the  relation  of  construction  to  success- 
ful lighting  may  be  of  further  interest  and  will  help  to  convince 
the  architect  that  he  is  a  large  factor  in  lighting. 


120  THE  LIGHTING  ART 

The  optical  characteristics  of  skylight  glass  are  of  great  im- 
portance if  artificial  light  is  to  be  projected  through  it  or  diffused 
by  it.  Ornamental  designs  in  ceilings  might  better  be  laid  out 
in  accordance  with  the  best  spacing  of  outlets  wherever  this  is 
possible  because  in  most  cases  the  fixtures  are  supported  in  a 
manner  symmetrical  with  the  design.  The  distribution  of 
light  from  a  fixture  may  in  some  cases  be  adapted  to  the  design 
with  artistic  results.  Many  places  can  be  provided  by  the 
architect  for  concealing  light-sources  if  such  a  plan  of  lighting 
appears  to  be  most  desirable.  False  beams,  cornices,  moldings, 
recesses  in  the  walls,  ceiling,  pilasters  or  above  capitals,  or 
other  ornamental  details  may  be  woven  into  the  decorative 
scheme  if  these  are  necessary  in  order  to  provide  the  best  light- 
ing effect.  There  are  cases  on  record  where  such  cooperation 
has  resulted  in  unique  effects  which  are  highly  satisfactory. 
Sometimes  the  architect  has  apparently  been  so  oblivious  to 
the  lighting  requirements  that  he  has  placed  a  network  of 
structural  beams  above  and  close  to  the  subskylights,  thus 
placing  insurmountable  obstacles  in  the  way  of  the  lighting 
expert. 

In  show-windows  the  architect  should  understand  the  influ- 
ence of  dimensions  upon  the  lighting  effect;  he  should  supply 
places  for  concealing  the  lighting  units;  and  he  should  under- 
stand the  possibilities  of  lighting  sufficiently  to  supply  the 
proper  abundance  of  outlets  and  circuits.  Such  details  as 
ventilating  grills  are  sometimes  placed  in  positions  which  cause 
difficulties  in  the  spacing  of  lighting  units. 

In  beautiful  interiors  of  the  purer  types  of  architecture  there 
are  perhaps  still  more  urgent  reasons  for  the  early  consideration 
of  the  lighting  by  the  architect.  After  the  building  is  com- 
pleted the  ingenuity  of  the  lighting  specialist  may  be  depended 
upon  to  provide  illumination  but  he  cannot  always  obtain  the 
effect  which  would  be  most  desired  because  he  is  limited  to  a 
few  places  where  outlets  have  been  provided  or  where  they  may 
be  installed  and  by  other  obstacles.  Furthermore,  it  may  be 
beyond  the  bounds  of  possibility  to  design  a  fixture  which 
properly  distributes  the  light  and  at  the  same  time  meets  the 
requirements  of  period  style  or  artistic  appearance.  Often  it 


LIGHTING  AND  ARCHITECTURE  121 

is  most  desirable  to  eliminate  visible  fixtures  and  obviously  in 
such  cases  it  is  necessary  to  provide  places  for  concealing  the 
lighting  units.  In  viewing  the  results  of  lighting  as  related  to 
architecture  many  admirable  examples  are  found  in  which  the 
indirect  system  of  lighting  from  concealed  sources  has  been 
utilized.  Not  infrequently  has  it  been  found  that  electric 
wiring  is  insufficient  in  carrying  capacity  although  usually  this 
may  be  remedied.  Among  the  vast  number  of  details  pertain- 
ing to  lighting  the  architect  should  bear  in  mind  that  the  sys- 
tem should  be  readily  maintainable  in  efficient  operation. 
For  this  reason  provisions  should  be  made  for  easy  access  to  the 
lighting  units.  This  is  often  a  matter  of  primary  construction. 

Besides  the  usual  lighting  requirements  the  architect  may 
consider  many  of  the  more  unique  uses  of  light  for  special 
decorative  effects.  As  an  example  in  an  interior  the  large  basin 
of  a  fountain  in  the  center  of  the  room  was  very  dark  at  night 
owing  to  the  unusual  lighting  plan  which  was  found  to  be 
suitable  for  the  room.  No  provision  had  been  made  for  illu- 
minating the  fountain  so  it  was  necessary  to  cut  a  hole  in  the 
ceiling  about  forty  feet  above  the  floor  and,  by  means  of  an 
optical  system,  to  project  a  very  narrow  cone  of  light  down- 
ward just  covering  the  basin  of  the  fountain.  This  provided 
an  excellent  solution  which  is  a  testimonial  of  the  ingenuity 
of  the  lighting  specialist. 

Uniformity  in  brightness  or  in  illumination  is  often  quite 
necessary  and  sometimes  this  is  difficult  to  obtain  over  a  large 
area  such  as  a  wall  or  ceiling.  However,  it  appears  that  striv- 
ing for  uniformity  is  sometimes  a  misdirected  effort.  Some  of 
the  most  charming  effects  of  light  and  shade  are  due  to  asym- 
metrical distribution  of  light  in  the  room  as  a  whole.  In  some 
cases  such  a  distribution  of  brightness  or  illumination  on  a  wall 
produces  very  artistic  effects.  A  case  in  poirit  is  that  of  a  large 
mural  painting  which  may  be  beautified  by  a  .proper  asym- 
metrical distribution  of  illumination  over  its  surface. 

In  this  brief  discussion  of  an  extensive  subject  color  has  been 
given  little  consideration.  The  points  discussed  are  some  of 
those  of  immediate  importance.  The  potentiality  of  the  charm 
of  color  in  lighting  has  been  barely  tapped  and  a  great  future 
appears  to  be  open  for  this  aspect  of  lighting. 


CHAPTER  XV 
THE  PORTABLE  LIGHTING-UNIT 

The  portable  lamp  is  such  an  important  factor  in  lighting 
and  the  possibilities  of  utilizing  it  more  widely  in  lighting 
effects  are  so  promising  that  it  appears  of  interest  to  discuss 
it  independently.  Two  marked  features  of  improper  lighting 
are  the  prevalence  of  improper  lighting  fixtures  and  the  usual 
simplicity  of  the  remedies  for  converting  such  fixtures  into 
satisfactory  ones.  Although  the  remedy  may  be  simple  it  is 
seldom  applied  because  the  salesman  and  consumer  are  un- 
acquainted with  the  simple  laws  of  light.  But  there  is  another 
reason  which  is  a  serious  one  in  all  phases  of  lighting,  namely, 
the  indifference  of  the  average  person  to  the  possibilities  of 
lighting. 

There  are  distinctly  two  viewpoints  for  the  consideration  of 
most  portable  lamps,  namely,  the  purely  utilitarian  and  the 
artistic.  These  are  intimately  interwoven  but  certain  scientific 
principles  may  be  separated  and  discussed.  Incidentally  the 
artistic  aspect  is  very  prominent  in  portable  lamps  because  the 
purely  utilitarian  "desk-lamp"  is  rapidly  disappearing  from 
use  with  the  increasing  tendency  toward  general  lighting  in 
those  places  where  it  has  been  widely  used  in  the  past.  How- 
ever, the  portable  unit  is  becoming  more  popular  in  much  in- 
terior lighting  where  variety  in  artistic  lighting  effects  is  recog- 
nized, at  least  feebly,  as  the  source  of  much  pleasure. 

It  is  interesting  to  invade  fixture  stores  as  a  purchaser  and  to 
study  the  manner  in  which  portable  lamps  are  discussed.  This 
applies  to  nearly  all  fixtures  with  the  exception  of  the  purely 
utilitarian  such  as  industrial  units.  The  salesman  discusses 
chiefly,  and  often  solely,  the  artistic  value  of  the  portable  lamp. 
It  is  true  that  many  units  are  purchased  for  the  chief  purpose 
of  supplying  a  source  of  light  which  serves  its  purpose  by  acci- 
dental distribution  but  most  of  these  units  are  also  intended  to 

122 


THE  PORTABLE  LIGHTING-UNIT  123 

supply  illumination  for  a  specific  purpose  such  as  for  reading  at 
a  library  table  or  for  seeing  music  on  a  piano.  Seldom  does 
a  person  encounter  a  salesman  who  demonstrates  the  distribu- 
tion of  light  from  a  portable  lamp  by  means  of  a  library  table, 
a  chair  and  a  book  or  by  holding  music  near  a  floor  lamp  at  about 
the  position  which  it  will  occupy  under  actual  conditions. 

A  small  percentage  of  decorative  portable  lamps  are  fit  for 
their  intended  utilitarian  purpose  although  it  is  gratifying  to 
note  that  during  the  past  few  years  a  number  of  excellent  de- 
signs have  appeared.  That  a  portable  lamp  may  be  artistic 
and  yet  utilitarian  certainly  cannot  be  questioned.  However, 
this  is  not  a  discussion  of  esthetics,  except  indirectly,  as  it  is 
usually  the  attempt  to  realize  the  artistic  that  defeats  the 
realization  of  the  utilitarian  goal. 

The  utility  of  a  portable  lamp  is  largely  a  matter  of  dimen- 
sions of  the  various  parts  and  in  order  to  illustrate  this  and  bring 
forth  various  points  of  interest  a  few  diagrams  will  be  used. 
These  should  serve  the  purpose  of  emphasizing  to  those  con- 
cerned, the  extreme  simplicity  of  the  principles  of  fixtures  of 
this  character.  In  order  to  analyze  the  portable  lamp,  the 
library  lamp  will  be  considered  on  the  basis  of  certain  definite 
assumptions  regarding  the  positions  of  the  eyes  and  of  the 
book  which  it  is  assumed  a  person  is  reading.  The  position 
of  the  book,  B,  in  the  accompanying  diagrams,  is  assumed  to  be 
30  inches  from  the  vertical  axis  of  the  lamp  and  at  the  level 
of  the  top  of  the  table  which  is  30  inches  above  the  floor.  The 
position  of  the  eyes,  E,  is  taken  as  12  inches  above  the  level 
of  the  top  of  the  table  and  is  designated  by  VE,  the  vertical 
height  V  of  the  eyes  E  above  the  plane  of  the  top  of  the  table. 
The  light-source  is  designated  by  S,  its  height  above  the  plane 
of  the  lower  aperture  of  the  shade  by  h,  and  above  the  top  of 
the  table  by  F5,  and  the  horizontal  distance  from  the  extreme 
edge  of  the  aperture  of  the  shade  to  the  vertical  axis  of  the 
unit  by  R.  Several  variables  with  different  types  of  shades  are 
considered  in  the  following  simple  diagrams.  The  light-source 
is  assumed  to  be  of  small  dimensions  but  if  it  is  not,  certain 
obvious  alterations  must  be  made.  (See  Fig.  32.) 

In  Fig.  28  the  effect  of  the  height  of  the  lamp  pedestal  is 


124 


THE  LIGHTING  ART 


FIG.  28. — Influence  of  the  height  of  a  shade. 


FIG.  29. — Influence  of  position  of  the  light-source  in  a  shade. 


THE  PORTABLE  LIGHTING-UNIT  125 

shown.  The  light-source  is  assumed  to  be  confined  to  a  point 
but  for  practical  applications  when  the  eyes  at  E  are  considered, 
the  lowest  point  of  the  ordinary  extended  light-source  is  used 
in  such  a  diagram  and  for  the  book,  B,  the  highest  point  of  the 
light-source  is  used.  A  primary  aim  should  be  to  confine  the 
direct  rays  from  the  light-source  below  the  point  E.  It  is 
seen  that  the  increase  in  the  height  of  the  pedestal  raises  the 
limiting  ray  to  an  undesirable  position.  If  the  two  limiting 
rays  (from  the  highest  and  lowest  portions  of  the  light-source) 
are  confined  so  as  to  cut  the  vertical  line  between  E  and  B  the 
lamp  is  satisfactory  from  this  viewpoint.  It  should  be  noted 
that  the  book  and  the  eyes  are  considered  to  be  approximately 
in  a  plane  perpendicular  to  this  page. 

In  Fig.  29  is  shown  the  effect  of  varying  the  height  h  of  the 
light-source  above  the  plane  of  the  lower  aperture  of  the  shade. 
The  two  lower  positions  of  the  light-source  S%  and  S$  are  satis- 
factory provided  the  limiting  direct  ray  from  the  lower  point 
of  the  source  does  not  cross  the  vertical  line  as  high  as  E. 
In  such  mushroom  types  of  shades  it  is  a  common  error  to  have 
the  light-source  too  high  in  the  shade  as  shown  by  Si. 

In  Fig.  30  is  illustrated  the  common  shallow  type  of  shade 
which  does  not  confine  the  limiting  direct  ray  below  E.  Such 
shades  give  a  desirable  spread  of  light  but  if  the  pedestal  is 
too  high  it  is  necessary  to  sit  so  far  away  in  order  to  have 
the  limiting  direct  rays  fall  below  the  eye-level  that  the  illumi- 
nation is  too  low  for  comfortable  reading.  By  shortening  the 
pedestal  in  this  case  a  satisfactory  reading  lamp  may  be 
obtained. 

In  Fig.  31  are  shown  the  results  obtained  with  two  light- 
sources  in  the  same  shade.  If  it  is  desired  to  utilize  the  light 
from  both  sources,  the  source  S*  at  the  greater  distance  from 
the  eye  (greater  effective  jR2)  is  the  important  one  from  the 
standpoint  of  the  eye  and  source  Si  is  the  important  one  from 
the  standpoint  of  illuminating  the  book.  In  this  case  if  both 
lamps  are  to  contribute  to  the  illumination  the  limiting  rays 
of  both  of  them  must  be  confined  between  B  and  E  for 
satisfactory  results. 

These  diagrams  cover  the  important  variables  in  the  dimen- 


126 


THE  LIGHTING  ART 


FIG.  30. — Influence  of  size  of  the  aperture  of  a  shade. 


FIG.  31. — Effect  of  two  light-sources  in  a  shade. 


THE  PORTABLE  LIGHTING-UNIT 


127 


sions  of  library  lamps  and  though  simple  they  will  bear  some 
study.  The  various  relations  have  been  brought  together  in 
Fig.  32,  the  dimensions  being  shown  at  the  right.  The  rela- 
tion between  the  ratio  of  R  (one-half  the  maximum  width  of  the 
aperture)  to  the  height  h  of  the  light-source  above  the  plane  of 
the  aperture,  and  the  height  Vs  of  the  source  above  the  top  of 
the  table  is  shown  by  the  curve  for  satisfactory  portable  lamps 


4 

FIG.  32 


a  l£  /6  20  S4  £6  «  J6  40 

t&  fJie/fHT   Of  Jot/f?Cf  X/V  /Nftt£3 

— Summary  of  effect  of  dimensions  of  portable  lamps. 


for  reading  tables.  When  VE  =  12  inches  the  limiting  direct 
ray  just  enters  the  eye  at  E.  Another  height  of  limiting  direct 
rav>  VE  =  6  inches,  is  considered  in  the  middle  curve.  On  the 
curve,  VE  =  0,  the  condition  at  B  is  considered.  From  these 
curves  it  is  easy  to  determine  whether  or  not  a  library  lamp 
of  certain  dimensions  meets  the  requirements  of  the  foregoing 
assumptions.  It  appears  that  for  ordinary  light-sources  if  the 
measurements  are  made  to  the  middle  vertical  point  of  the 
light-source  and  referred  to  the  middle  curve,  satisfactory  re- 
sults are  obtained.  These  curves  are  not  proposed  as  a  guide 
to  be  used  in  the  censorship  of  library  lamps  although  they  may 


128  THE  LIGHTING  ART 

be  used  in  this  manner.  They  are  presented  as  a  brief  summary 
of  a  diagrammatic  discussion  of  the  principles  underlying  the 
design  of  utilitarian  library  lamps.  Many  phases  of  lighting 
may  be  considered  in  a  similar  graphical  manner  with  edifying 
results. 

For  the  sake  of  simplicity  the  ordinary  "  direct "  type  of  porta- 
ble lamp  has  been  considered  in  the  foregoing;  however,  greater 
possibilities  in  lighting  are  found  in  the  use  of  portable  units 
from  which  different  distributions  of  light  may  be  obtained. 
As  has  already  beem  emphasized,  portable  lamps  are  extremely 
adaptable  to  obtaining  a  variety  of  artistic  lighting  effects  as 
well  as  to  satisfying  various  utilitarian  requirements.  If  they 
are  provided  with  means  for  obtaining  at  least  two  independent 
distributions  of  light  (and  a  combination  of  the  two)  the  flexi- 
bility of  the  lighting  is  greatly  augmented.  One  of  the  greatest 
drawbacks  in  the  adoption  of  portable  lamps  for  general  light- 
ing purposes  in  the  home  is  the  common  scarcity  of  electrical 
or  gas  outlets. 

There  are  sufficient  reasons  for  designing  portable  lamps 
which  incorporate  various  scientific  aspects  in  the  control  of 
light.  Within  the  past  few  years  a  number  of  excellent  designs 
have  appeared  upon  the  market  and  though  portable  lamps  are 
extensively  used  at  present,  it  appears  that,  with  the  develop- 
ment of  units  of  greater  adaptability  and  variety  in  the  light- 
ing effects  obtainable,  they  will  be  much  more  widely  used  in 
the  future  not  only  for  residential  lighting  but  for  many  other 
fields. 

In  Fig.  33  a  very  commendable  principle  is  shown  incor- 
porated in  the  portable  lamp.  The  light-source  is  shielded  by 
means  of  an  inverted  reflector  R  which  may  be  either  opaque 
or  of  dense  opal  glass.  If  the  reflector  is  opaque  the  light  is 
reflected  to  the  inner  surface  of  the  shade  S  which  is  coated  with 
a  diffusing  medium  such  as  flat  white  paint.  The  effective 
light-source — the  inner  surface  of  the  shade — is  of  large  area 
and  therefore  may  be  of  low  brightness  for  a  given  illumina- 
tion at  the  point  of  interest.  This  is  especially  desirable  when 
the  eyes  are  obliged  to  view  glazed  surfaces  such  as  varnished 
table-tops  or  calendered  paper  for  the  glare  from  such  surfaces 


THE  PORTABLE  LIGHTING-UNIT 


129 


is  very  marked  when  the  reflected  images  of  light-sources  are 
of  high  brightness.  This  glare  is  materially  reduced  and  is 
often  entirely  absent  when  the  effective  light-source  is  of  low 
brightness  as  in  this  case.  The  shade  may  be  of  metal  into 
which  decorative  patterns  have  been  etched  or  cut.  In  the 
latter  case  the  openings  may  be  covered  on  the  inside  with  a 
dense  translucent  material.  If  the  reflector  R  is  of  dense  opal 
glass  the  unit  is  somewhat  more  efficient  but  unless  the  glass  is 


PIG.  33. 


PIG.  35.  FIG.  36. 

PIGS.  33  to  36. — Recent  progress  in  the  design  of  portable  lamps. 

very  dense  it  must  be  shielded  from  the  eyes,  for  example,  by 
means  of  a  deeper  shade,  S,  which  reduces  the  effectiveness  of 
the  light  reflected  from  the  inner  surface  of  the  shade. 

Another  type  of  portable  lamp  is  shown  in  Fig.  34  in  which  a 
diffusing  glass  reflector  R  is  inverted.  Upon  this  a  shade  5. 
usually  of  silk,  is  supported.  The  distribution  of  light  from 
this  is  a  combination  of  an  indirect  component  with  a  direct 
component.  In  this  lamp  the  inner  shade  may  be  of  light- 
density  opal  glass  because  it  is  possible  to  shield  it  from  the  eyes 


130  THE  LIGHTING  ART 

without  seriously  reducing  the  effectiveness  of  the  unit  as  a 
reading  lamp.  The  distribution  of  light  is  pleasing  but  lacks 
the  element  of  variety.  When  the  silk  is  of  a  saturated  color 
or  of  a  dark  shade  it  is  advantageous  to  provide  an  inner  lining 
of  white  or  of  a  highly  reflecting  tint. 

In  Fig.  35  is  shown  a  modification  of  the  foregoing  principle 
which  has  the  advantage  of  variety  in  distribution.  Such  a 
unit  has  appeared  in  a  very  practicable  design  but  the  principle 
is  illustrated  here  in  a  simple  manner  by  the  use  of  two  opal 
glass  reflectors  placed  one  above  the  other  and  each  containing 
one  or  more  light-sources.  If  the  upper  source  is  lighted,  the 
resulting  light  is  a  combination  of  indirect  and  direct  compo- 
nents. If  only  the  lower  sources  are  lighted  the  indirect  compo- 
nent is  smaller  and  the  direct  light,  which  consists  of  that  trans- 
mitted by  the  lower  reflector  and  reflected  from  the  lower 
surface  of  the  upper  reflector  and  from  the  silk  shade,  is  greater 
in  magnitude.  It  is  seen  that  this  unit  possesses  a  certain 
adaptability  not  possessed  by  the  ordinary  lamp. 

In  Fig.  36  is  shown  a  simple  but  excellent  type  of  portable  lamp 
which  may  be  used  to  illuminate  a  small  area  for  reading  or  for 
decorative  purposes  or  by  means  of  the  indirect  component  an 
entire  room  may  be  flooded  with  light.  The  upper  reflector  is 
opaque  and  preferably  silvered  inside.  If  a  lamp  of  high  lumin- 
ous output  is  used  in  this  reflector  a  large  area  may  be  indi- 
rectly lighted  to  a  satisfactory  intensity.  Several  opal  or 
frosted  lamps  may  be  used  for  the  direct  component.  A  small 
portion  of  the  light  from  the  upper  source  is  permitted  to  escape 
from  the  lower  part  of  the  reflector  and  this  light  is  scattered  in 
different  ways  thus  serving  to  illuminate  the  silk  shade.  One 
of  these  is  illustrated  by  the  opal  glass  diffuser  D.  Tinted 
lamps  or  color-filters  may  be  used  for  obtaining  the  desired 
colored  light.  By  means  of  such  a  unit  the  distiibution  and 
color  of  light  may  be  readily  adapted  to  suit  the  mood  or  spirit 
of  the  occasion  or  to  meet  the  utilitarian  requirements. 

Many  combinations  of  principles  may  be  incorporated  into 
portable  lamps  of  which  the  foregoing  illustrations  represent 
a  few  possibilities.  The  ease  with  which  silk  and  other  fabrics 
may  be  utilized  for  shades  and  reflectors  make  it  possible  with 


THE  PORTABLE  LIGHTING-UNIT  131 

the  aid  of  wire  frames  to  design  many  unique  lamps  for  special 
purposes  besides  providing  notes  of  color  as  well  as  floods  of 
tinted  light  obtained  by  transmission  and  by  reflection.  By 
such  means  those  who  possess  an  esthetic  sense  for  color  may 
enjoy  the  pleasures  of  "painting  with  light."  Besides  provid- 
ing localized  and  general  lighting  for  ordinary  purposes,  special 
reflectors  may  be  concealed  in  such  units,  or  certain  panels  may 
be  omitted  from  the  shade  in  order  to  illuminate  special  objects 
such  as  paintings  by  means  of  direct  light  from  a  unit.  Porta- 
ble lamps  need  not  be  limited  to  the  use  of  the  ordinary  sym- 
metrical shade,  for  half-shades  may  be  used  to  conceal  the  light- 
source  or  other  equipment  from  the  eyes  while  from  the  open 
half,  a  wall,  painting,  book-case,  or  other  area  may  be  illumi- 
nated directly.  Portable  lamps  are  readily  adaptable  to 
obtaining  assymetrical  distribution  of  light  as  well  as  color 
which  ordinarily  are  the  requisites  of  artistic  as  well  as  econom- 
ical lighting  in  many  interiors.  The  potentiality  of  the  porta- 
ble lamp  can  hardly  be  overrated  and  it  is  to  be  hoped  that 
designs  for  lighting  in  the  future  will  make  it  possible  to  reap 
the  pleasures  from  the  use  of  such  units  by  providing  an  abun- 
dance of  outlets  which  certainly  cannot  be  denied  on  the  grounds 
of  cost  because  the  expense  of  such  outlets  is  insignificant  com- 
pared with  their  importance.  Observations  in  average  apart- 
ments, houses,  and  other  interiors  in  which  the  portable  lamp 
is  especially  adaptable  lead  to  the  conclusion  that  such  outlets 
are  far  too  rare.  The  architect  and  electrical  contractor  can 
do  much  to  remedy  this  deficiency. 


CHAPTER  XVI 
RESIDENCE  LIGHTING 

For  several  reasons  the  lighting  of  the  home  is  among  the 
most  important  aspects  of  lighting.  It  is  of  primary  interest 
to  the  lighting  specialist  because  it  is  in  the  home  that  the 
science  and  art  of  lighting  may  reach  mankind  in  general  if  the 
opportunities  are  provided.  Proper  lighting  contributes  more 
to  the  attractiveness  of  a  home  than  is  commonly  suspected 
and  the  greatest  obstacle  which  must  be  removed  is  the  indif- 
ference of  mankind  in  general  to  the  potentiality  of  lighting. 
This  indifference  will  succumb  only  to  enlightenment  which 
must  arise  from  the  cooperative  efforts  of  the  lighting  specialist, 
the  architect,  the  decorator,  the  contractor,  the  fixture  dealer, 
and  the  central-station  representative.  The  central-station 
should  have  a  primary  interest  in  the  satisfaction  gained  by  the 
householder  from  proper  lighting.  There  are  many  million 
homes  in  this  country  wired  for  electricity  or  piped  for  gas  and 
the  householder  receives  an  invaluable  legacy  from  well- 
directed  efforts  of  the  representative  of  the  central-station  in 
the  cause  of  good  lighting.  The  central-station  may  profit 
either  through  increased  load  or  through  a  satisfied  and 
interested  consumer. 

The  architect  is  often  a  factor  in  the  lighting  results  for  he 
may  be  responsible  not  only  for  the  outlets  and  the  decorative 
scheme  but  also  may  direct  the  selection  of  the  fixtures.  The 
potentiality  of  lighting  cannot  be  fully  enjoyed  without  having 
a  sufficient  supply  of  outlets  and  there  appears  to  be  no  just 
reason  for  not  providing  electric  or  gas  service  quite  liberally 
during  the  construction  of  a  building.  The  contractor  is 
often  a  factor  in  such  provisions  and  instead  of  curtailing  the 
expenditure  for  a  few  extra  outlets  which  may  not  be  put  into 
immediate  use,  it  is  not  only  to  his  advantage  but  also  to  that 

132 


RESIDENCE  LIGHTING  133 

of  the  householder  to  provide  outlets  generously.  One  of  the 
chief  criticisms  which  may  be  applied  to  residences  on  every 
hand  is  the  scarcity  of  lighting  outlets  for  without  a  generous 
supply  of  these  essentials,  the  possibilities  in  lighting  cannot 
be  fully  realized.  If  the  householder  is  provided  with  fixtures 
which  are  so  equipped  and  wired  that  variety  in  distribution  and 
color  of  light  may  be  obtained  he  will  awaken  to  the  utili- 
tarian and  artistic  values  of  lighting.  Plenty  of  outlets  for 
connecting  portable  lamps  is  also  a  factor  in  overcoming  the 
general  indifference  of  users  of  light  in  the  home. 

The  part  that  the  fixture-dealer  and  salesman  play  in  this 
propaganda  for  the  consumer's  good  has  already  been  touched 
upon  as  well  as  that  of  the  decorator  and  the  place  which  may  be 
filled  by  the  lighting  specialist  is  quite  evident.  The  foregoing 
has  been  introduced  as  a  preface  to  this  chapter  because  it 
appears  to  be  very  important.  Proper  lighting  in  the  home  is 
dependent  upon  those  who  provide  outlets  and  fixtures  and  upon 
those  who  are  in  a  position  to  enlighten  the  general  public  re- 
garding the  importance  of  good  lighting  in  contributing  to  the 
welfare  and  happiness  of  the  occupants  of  the  home. 

There  are  important  hygienic  aspects  of  lighting  in  the  home 
but  the  greater  possibilities  lie  in  making  the  home  cheerful  and 
attractive.  No  modern  light-source  should  be  exposed  so  as  \ 
to  be  normally  visible.  Such  a  condition  is  harmful  to  vision 
and  contributes  much  toward  making  a  home  unattractive. 
In  passing  along  a  street  at  night  close  to  residences  it  is  not 
unusual  to  note  lightings  which  might  readily  be  considered  to 
be  punishments  illy  disguised.  Although  those  who  live  in  such 
environments  may  be  unconscious  of  the  ill  effects  of  such 
lighting  conditions,  these  doubtless  leave  their  imprint  upon 
the  health  and  disposition  of  these  persons.  A  living  room  may 
be  lighted  by  means  of  an  inartistic  fixture  containing  exposed 
light-sources  and  the  lighting  effects  may  be  harsh  and  lacking 
in  any  of  the  essentials  of  esthetics.  If  a  reading  lamp  con- 
tains a  bright  light-source  which  is  unshaded  from  the  eyes, 
annoyance  to  vision,  discomfort,  and  even  ill  temper  may  result. 
On  the  other  hand,  well-designed  fixtures  cannot  produce  a  rest- 
ful lighting  unless  aided  by  a  decorative  scheme  which  is  the 


134  THE  LIGHTING  ART 

result  of  the  application  of  good  taste  and  some  knowledge  of 
the  interdependence  of  lighting  and  decoration. 

There  are  few  places  for  bare  lamps  in  the  home  outside  of 
indirect  and  so-called  semi-indirect  (direct-indirect)  fixtures. 
Even  in  these  units  a  frosted  incandescent  lamp  or  a  diffusing 
envelope  for  a  gas  mantle  reduces  the  harshness  of  the  shadows 
on  the  ceiling  and  walls  which  often  result  from  bare  light- 
sources.  In  a  similar  manner  frosted  lamps  in  upright  shades 
on  brackets  produce  a  more  artistic  effect  than  bare  lamps. 
The  so-called  bowl-frosted  lamps  may  often  be  used  to  better 
advantage  in  pendant  shades,  in  showers,  or  in  other  fixtures 
and  rarely  is  a  bare  light-source  as  satisfactory  as  a  frosted 
or  opal  lamp  for  a  reading  lamp  even  though  the  light-source 
is  shielded  from  the  eyes.  The  glare  due  to  the  images  of  bare 
light-sources  which  are  reflected  from  polished  or  varnished 
furniture,  glazed  paper,  and  other  glossy  surfaces  is  usually 
more  severe  than  when  frosted  or  opal  lamps  are  employed. 

Even  though  the  fixtures  are  properly  designed  and  used 
there  may  be  other  harmful  physiological  and  psychological 
effects  attributable  to  improper  brightness-distribution.  For 
example,  the  brightness  of  a  lighting  accessory,  such  as  a  glass 
shade,  will  be  glaring  amid  dark  surroundings  even  though  it 
might  be  quite  satisfactory  amid  medium  or  light  surroundings. 
In  a  similar  manner  eye-fatigue  may  not  be  experienced  on  read- 
ing while  facing  a  wall  of  medium  brightness  but  under  the  same 
distribution  of  light  extreme  fatigue  may  result  if  the  wall  is 
of  very  low  reflection-factor.  While  reading  at  a  library  table 
by  means  of  the  illumination  from  a  well-designed  portable  lamp 
the  visual  field  surrounding  the  book  may  be  of  a  medium 
brightness  and  the  conditions  perhaps  will  be  quite  satis- 
factory. If  the  remainder  of  the  room  is  in  semi-darkness  the 
psychological  effect  is  usually  conducive  to  concentration  of 
attention  and  the  semi-darkness  provides  a  place  toward  which 
the  eyes  may  be  directed  occasionally  for  the  purpose  of  resting 
them.  These  and  other  details  are  of  importance  in  the  welfare 
of  vision. 

It  is  a  difficult  matter  to  discuss  the  esthetic  aspects  of 
lighting  in  the  home  because  this  involves  individual  taste 


RESIDENCE  LIGHTING  135 

which  is  more  or  less  indeterminate.  However,  the  artistic 
possibilities  of  lighting  are  so  extensive  and  important  that 
no  discussion  of  residence  lighting  can  avoid  the  treatment  of 
this  aspect.  There  are  certain  broad  esthetic  principles  which 
are  acceptable  and  it  should  be  of  interest  to  discuss  the  artistic 
aspect  of  lighting  even  though  the  points  brought  forth  may 
be  defended  only  on  the  grounds  of  an  individual  taste.  The 
variables  in  the  lighting  of  the  home  are  so  numerous  that  all 
of  them  cannot  possibly  be  discussed  here;  however,  an  attempt 
will  be  made  to  point  out  a  few  principles  and  possibilities. 

Inefficient,  unsafe,  and  inartistic  fixtures  found  in  residences 
may  be  discarded  for  the  same  reasons  that  any  other  unsatis- 
factory equipment  would  be  dispensed  with ;  therefore,  no  space 
need  be  given  to  a  discussion  of  the  vast  number  of  badly  de- 
signed fixtures  which  are  in  use  at  the  present  time.  Further- 
more, economy  in  lighting  is  of  minor  importance  compared 
with  the  utilitarian  and  artistic  satisfactoriness  of  lighting  in 
the  home.  The  cost  of  enjoying  satisfactory  lighting  in  the 
home  need  be  no  greater  than  the  cost  of  suffering  bad  lighting 
in  most  cases  and  any  reasonable  outlay  for  the  installation  and 
maintenance  of  good  lighting  in  the  home  is  justifiable. 

Inasmuch  as  the  various  rooms  in  a  home  present  different 
lighting  problems  they  will  be  briefly  treated  separately. 
Control  is  an  important  factor  in  lighting  and,  although  gas 
may  be  controlled  from  remote  switches,  for  convenience  this 
aspect  will  be  treated  as  though  the  systems  were  electrical. 
This  explanation  is  made  in  order  that  no  unjust  disparage- 
ment of  the  possibilities  of  gas  lighting  may  be  construed 
because  the  progress  which  has  been  made  by  designers  of  gas- 
lighting  accessories  must  always  be  viewed  with  admiration 
considering  the  difficulties  which  must  be  overcome. 

Living  Room. — It  appears  that  the  use  of  ceiling  fixtures  in 
the  living  room  is  not,  in  general,  as  conducive  to  artistic  light- 
ing effects  as  asymmetrical  arrangements  of  fixtures.  The  liv- 
ing room  should  present  a  restful  artistic  appearance  and  in  this, 
lighting  is  a  large  factor.  A  central  fixture  produces  a  sym- 
metry in  the  lighting  effect  which  lacks  variety  in  light  and 

shade  and  which  becomes  monotonous.     If  a  ceiling  fixture 
10 


136  THE  LIGHTING  ART 

is  used  it  should  be  provided  with  at  least  two  circuits  so  that 
the  intensity  of  illumination  may  be  controlled  to  some  degree. 
As  has  been  mentioned  before,  fixtures  from  which  two  or  more 
widely  different  distributions  of  light  can  be  obtained  should 
be  more  acceptable  than  the  ordinary  fixtures.  In  the  living- 
room,  more  than  in  any  other  room  in  the  home,  provisions 
should  be  made  to  adapt  the  lighting  to  the  individual  mood 
or  to  the  spirit  of  the  occasion.  Fixtures  provided  with  various 
circuits  which  control  different  distributions  of  light  are  essen- 
tial if  variety  in  lighting  is  to  be  obtained  from  ceiling  fixtures. 

If  ordinary  central  fixtures  are  used  the  type  is  quite  a 
matter  of  taste.  If  a  shower  is  used  it  should  be  hung  high,  the 
shades  should  be  deep  and  of  low  transmission-factor  and  no 
exposed  light-source  should  be  visible.  If  the  so-called  semi- 
indirect  bowl  is  employed  the  glass  should  ordinarily  be  very 
dense  opal  or  should  be  otherwise  highly  diffusing  and  of  low 
transmission-factor.  It  should  be  hung  as  high  as  it  is  prac- 
ticable. Purely  indirect  central  fixtures  do  not  appear  to  be 
as  generally  adaptable  to  living  rooms  as  some  other  units 
although  fixtures  from  which  an  indirect  component  can  be 
obtained  when  desired  are  found  to  be  convenient  and  de- 
sirable lighting  accessories.  Being  largely  a  matter  of  taste, 
it  is  unwise  to  attempt  to  condemn  the  central  fixture  but  atten- 
tion will  be  directed  to  other  means  of  lighting  the  living  room 
which  provide  greater  variety  in  effects.  It  appears  to  the 
author  that  there  are  certain  objections  which  may  be  applied 
to  the  central  fixture  in  many  cases  among  these  being  the 
monotonous  symmetry  in  the  lighting  effect,  the  prominence 
of  the  fixture  and  the  accompanying  annoyance  even  from  the 
mild  glare  from  many  fairly  well-designed  units,  and  the 
distraction  from  the  beauty  of  the  room  as  a  whole,  especially 
if  the  ceilings  are  low.  It  appears  to  be  likely  that  the  use  of 
ceiling  fixtures  in  living  rooms  of  fair  size  will  decrease,  how- 
ever, in  planning  a  residence  it  is  a  wise  plan  to  provide  wiring 
for  ceiling  outlets  even  though  they  are  not  to  be  used  initially. 

Brackets  in  which  the  light-sources  are  shaded  by  silk  shades 
or  by  dense  diffusing  glass  provide  a  means  for  asymmetrical 
lighting  effects  and  are  of  decorative  value.  If  the  background 


RESIDENCE  LIGHTING  137 

i 

is  of  low  reflection-factor  these  units  must  be  of  very  low 
brightness  in  order  to  avoid  glare.  A  common  mistake  is  to 
place  light-sources  of  too  high  luminous  output  in  small  shades. 
Considering  the  light-source  to  be  confined  to  a  point  and  sur- 
rounded by  a  spherical  shade  of  diffusing  glass,  it  is  obvious 
that  the  brightness  of  the  latter  will  vary  inversely  as  the  square 
of  the  diameter  of  the  shade  for  a  light-source  of  a  given 
luminous  output.  Where  the  appearance  of  the  unit  permits 
their  use,  large  shades  should  be  used.  In  fact,  it  is  surprising 
how  large  the  shades  may  be  sometimes  and  still  be  appropriate. 
An  opal  glass  shade  6  inches  in  diameter  containing  a  25-watt 
tungsten  lamp  is  commonly  of  a  limiting  brightness  as  viewed 
against  a  fairly  bright  wall  even  when  the  glass  is  of  a  moderate 
density.  Brackets  are  conveniently  controlled  by  means  of 
switches  attached  to  them  with  the  exception  of  those  which 
cannot  be  reached  easily  as  might  be  the  case  with  mantle 
brackets. 

The  baseboard  and  floor  outlets  are  the  most  important  in 
the  living  room  from  the  standpoint  of  general  adaptability 
of  the  lighting  to  suit  the  desires  of  the  householder.  Never- 
theless such  outlets  are  often  the  most  neglected  features  in  the 
plans  for  lighting  service.  In  a  living  room  of  moderate  size 
five  and  even  ten  outlets  chiefly  in  the  baseboard  may  be  justi- 
fied. Outlets  on  the  mantle  and  above  built-in  bookcases 
and  in  various  special  places  provide  convenient  connections 
for  decorative  lamps.  Many  places  may  be  found  for  con- 
cealing light-sources  such  as  in  vases  and  in  other  ornaments. 
Portable  lamps  may  be  obtained  in  many  designs;  they  may  be 
equipped  with  silk  shades  or  with  tinted  lamps;  they  may  be 
placed  in  various  positions  in  relation  to  each  other  or  to  the 
furnishings;  and  they  may  be  controlled  at  will.  All  of  these 
features  and  others  conspire  to  make  this  method  of  lighting  the 
living  room  exceedingly  attractive.  Variety  and  adaptability 
are  represented  by  such  a  system  to  a  higher  degree  of  perfec- 
tion than  by  any  other  scheme.  A  single  unit  with  a  powerful 
indirect  component  will  illuminate  a  fairly  large  room  and  utili- 
tarian and  decorative  spots  of  light  can  be  obtained  wherever 
desired.  Surely  no  other  method  of  lighting  the  living  room 


138  THE  LIGHTING  ART 

offers  such  possibilities  for  gleaning  from  lighting  all  of  its  poten- 
tial value.  Portable  lamps  are  the  most  wieldy  lighting  tools 
for  painting  with  light  but  the  urgent  need  is  for  outlets  to 
which  they  may  be  connected  conveniently. 

Dining  Room. — The  problem  of  lighting  the  dining  room  is 
more  definite  than  that  of  the  living  room.  The  table  is  con- 
fined to  a  fixed  position  and  it  may  be  taken  as  the  most  im- 
portant spot  in  the  room.  We  immediately  approach  a  psycho- 
logical aspect  of  lighting  and  it  appears  to  be  the  verdict  of 
many  who  study  lighting  that  the  table  should  be  the  most 
intensely  illuminated  object  in  the  room.  Certainly  there  is  a 
cheerfulness  about  a  well-illuminated  table  hemmed  in  by  semi- 
darkness.  If  this  is  the  principle  of  lighting  acceptable  for  the 
dining  room,  certain  types  of  lighting  do  not  meet  the  require- 
ments. The  size  of  the  dining  room  and  the  range  in  the 
number  of  diners  are  important  factors  to  be  considered. 

The  so-called  semi-indirect  units  ordinarily  flood  the  entire 
room  with  light  and  the  table  is  not  the  most  highly  illuminated 
spot  in  the  room  and  it  is  seldom  the  brightest  spot.  This  sys- 
tem does  not  appear  to  fill  the  requirements  for  the  best  light- 
ing in  the  dining  room;  however,  it  is  widely  in  use.  Although 
individual  taste  is  a  large  factor,  it  is  predicted  that  many 
persons  who  are  now  using  the  so-called  semi-indirect  fixture 
would  abandon  it  in  favor  of  a  modern  unit  which  directed 
the  dominant  light  to  the  table  area  if  they  were  provided  with 
an  opportunity  to  compare  the  two  lighting  effects. 

In  large  dining  rooms,  the  use  of  wall-brackets  may  possibly 
be  justified  if  candlesticks  on  the  table  provide  additional  il- 
lumination. However,  it  is  difficult  to  provide  a  comfortable 
lighting  from  wall-brackets  without  taking  extreme  precautions 
to  reduce  the  brightness  of  the  unit  and  to  have  the  background 
sufficiently  bright  to  avoid  glare.  When  these  conditions  are 
satisfactory  the  result  usually  is  a  distribution  of  light  possessing 
a  dominant  indirect  component. 

In  order  to  carry  out  the  principle  of  confining  the  dominant 
light  to  the  table  area  it  is  necessary  to  employ  small  units  on 
the  table  or  to  suspend  a  fixture  from  a  point  on  the  ceiling 
above  the  table.  If  the  units  are  placed  on  the  table  they 


RESIDENCE  LIGHTING  139 

l 

should  be  low  in  order  not  to  obstruct  the  view  of  the  diners 
and  they  must  be  well-shaded  in  order  to  avoid  glare.  One  of 
the  chief  difficulties  in  their  use  is  in  obtaining  convenient 
outlets  for  connecting  them. 

The  dome  which  hangs  suspended  from  the  ceiling  has  sup- 
plied an  excellent  lighting  for  the  dining  table  for  many  years 
when  used  under  the  proper  conditions.  Its  popularity  is  on 
the  wane  but  it  has  served  well.  The  dome  must  be  hung 
sufficiently  high  in  order  not  to  interfere  with  the  view  across 
the  table  but  when  in  this  position  care  must  be  taken  to  con- 
ceal the  light-sources  from  view.  Some  of  the  principles  al- 
ready discussed  in  Chapter  XV  apply  to  the  dining  room  dome. 

Although  the  dome  provides  a  satisfactory  distribution  of 
light,  such  a  result  may  be  accomplished  by  means  cf  units 
which  are  more  satisfactory  or  modern  in  appearance.  The 
ordinary  shower  equipped  with  proper  pendant  shades  and 
bowl-frosted  lamps  may  be  so  hung  as  to  provide  a  distribution 
of  light  quite  similar  to  that  from  the  dome.  The  simple  prin- 
ciples shown  in  Fig.  4  may  be  applied  to  the  pendant  shades  of 
a  shower.  The  advantage  of  such  a  unit  may  be  shown  by 
means  of  a  specific  case.  Assume  the  fixture  to  be  supplied 
with  deep  pendant  shades  of  a  dense  yellow  opal  glass.  Such 
a  fixture  may  be  hung  high  without  annoying  glare  from  the 
light-sources  because  these  are  concealed  by  the  deep  shades  and 
the  dominant  light  is  downward,  the  spread  of  the  direct  cone 
of  light  from  the  aperture  of  each  shade  being  determined  by 
the  height  of  the  light-source  above  the  aperture  of  the  shade. 
The  faces  of  the  diners  which  are  about  15  inches  vertically 
above  the  edge  of  the  table  receive  the  warm  yellow  light  trans- 
mitted by  the  shades  as  well  as  some  of  the  unaltered  light ' 
which  is  reflected  from  the  table  covering  and  other  objects. 
The  room  in  general  under  these  conditions  is  much  less  in- 
tensely illuminated  than  the  table  which  is  a  pleasing  result. 
By  means  of  two  circuits  a  variety  in  intensity  of  illumination 
may  be  obtained  and  if  tinted  lamps  are  used  some  of  the  charm 
of  color  may  be  enjoyed. 

Sorrte  showers  are  supported  from  the  edge  of  an  opaque  disk 
or  opal  glass  bowl.  In  the  former  case  the  fixture  is  not  always 


140  THE  LIGHTING  ART 

equipped  with  an  outlet  above  this  opaque  disk  or  shallow  bowl 
in  order  to  obtain  an  indirect  component  but  this  may  be  done 
with  pleasing  results  for  appropriate  occasions.  The  indirect 
component  whether  from  an  opaque  or  opal  glass  bowl  is 
valuable  in  introducing  variety  of  distribution  and  color  of 
light. 

Some  chandeliers  equipped  with  upright  imitation  candles  and 
frosted  lamps  approach  in  distribution  of  light  that  which  is 
obtained  from  the  so-called  semi-indirect  bowl.  Sometimes 
the  shadows  are  objectionable  and  it  cannot  be  said  that  this 
unit  successfully  fulfills  any  specific  aim  over  the  dining  table. 
If  silk  shades  having  a  highly  reflecting  and  diffusing  inner 
surface  be  placed  over  the  frosted  lamps,  a  considerable  portion 
of  the  light  is  directed  downward  and  the  effect  as  a  whole 
may  be  quite  pleasing. 

Representative  types  of  units  and  the  chief  principles  of 
lighting  the  dining-room  have  been  discussed  but  the  possi- 
bilities in  lighting  the  dining  table  will  be  further  shown  by 
means  of  a  specific  unit  designed  to  meet  some  of  the  modern 
requirements.  A  diagram  of  this  unit  is  shown  in  Fig.  37. 
The  aims  were  to  obtain  a  dominant  light  upon  the  table  by 
means  of  a  unit  possessing  a  modern  appearance  and  to  intro- 
duce the  element  of  variety  in  distribution  and  color  of  light 
in  a  simple  manner  from  accessories  which  were  available  in 
white  opal  glass.  An  opal  glass  bowl,  20  inches  in  diameter 
was  chosen  because  it  had  a  "button"  in  the  center  4  inches  in 
diameter.  This  button  was  ground  off  until  a  hole  3^  inches 
in  diameter  was  made  and  in  this  hole  a  spun  metal  ring  R 
was  fitted  with  a  shoulder  which  supported  it  in  place.  An 
opal  shade  S  which  had  been  previously  chosen  of  a  proper 
depth  and  curvature  near  its  aperture  was  held  in  place  by  the 
ring  R,  and  the  socket  A.  By  means  of  the  rod  E  the  light- 
source  could  be  raised  or  lowered,  thus  controlling  the  solid- 
angle  of  the  direct  cone  of  light  J9,  which  illuminated  the  table 
to  a  sufficient  intensity.  The  outside  of  shade  5  was  toned  a 
warm  yellow  and  the  outside  of  the  large  bowl  B  was  decorated 
by  means  of  warm  colors.  The  unit  was  hung  so  that  there  is 
a  clearance  of  32  inches  between  it  and  the  top  of  the  table. 


RESIDENCE  LIGHTING 


141 


When  the  center  lamp  is  lighted  the  table  is  illuminated  by 
means  of  the  direct  cone  of  light  D  and  the  brightness  of  the 
bowl  B  is  very  low  owing  to  the  double  diffusion  of  light  by  5 
and  B.  The  bowl  B  appears  of  a  warm  color  and  this  tint  is 
evident  on  the  faces  of  the  diners. 

Incidentally  it  is  interesting  to  note  the  details  which  play 
a  part  in  lighting.     The  shade  S  was  chosen  with  the  lower  part 


\ 


FIG.  37. — A  unit  designed  for  tjie  dining  room. 


curved  as  shown  in  order  that  its  brightness  be  kept  as  low  as 
possible.  Owing  to  the  curvature,  this  lower  part  of  S  pre- 
sents but  a  small  projection  in  the  direction  of  the  light-source 
and  hence  does  not  become  very  bright.  In  order  that  the 
hole,  which  is  viewed  as  a  narrow  ellipse,  be  of  a  brightness 
comparable  to  the  bowl  B  the  lower  part  of  the  inside  of  shade 
S  was  toned  a  warm  gray  besides  being  chosen  of  the  curvature 
shown.  Four  small  lamps  L  were  placed  outside  of  S  near  the 


142  THE  LIGHTING  ART 

upper  aperture  of  B.  These  are  controlled  by  another  circuit 
and  sometimes  are  slightly  tinted.  Various  obvious  details  of 
adjustment  and  suspension  not  shown  in  the  illustration  com- 
pleted a  very  satisfactory  lighting  unit.  The  center  lamp 
may  be  a  modern  concentrated  filament  type  and  the  cone  may 
be  adjusted  to  fit  the  table-top.  It  was  found  that  an  ordinary 
incandescent  lamp  was  very  satisfactory  and  that  the  shadows 
due  to  the  direct  light  were  not  as  harsh  as  with  the  concen- 
trated filament.  Even  when  a  "  daylight "  lamp  is  used  in  the 
center  socket  the  bowl  B  will  appear  warm  in  color.  It  may 
not  suit  many  tastes  to  use  artificial  daylight  for  the  direct 
light  but  it  is  interesting  to  note  the  beauty  of  such  color 
schemes  as  butter,  paprika,  and  baked  potato  under  this  illu- 
minant  as  compared  with  their  appearance  under  ordinary  yel- 
lowish artificial  light.  The  latter  quality  of  light,  however, 
appears  to  be  more  pleasing  in  its  general  effect  in  the  dining 
room.  The  element  of  variety  is  obtained  both  in  color  and 
in  distribution  of  light  by  this  fixture  which  is  as  simple  as 
many  which  do  not  strive  for  such  effects.  The  three  distri- 
butions of  light  obtainable  are  shown  in  Fig.  37 ;  C  being  a  small 
upward  and  large  downward  component  obtained  when  only 
the  center  lamp  is  lighted;  L  being  obtained  from  the  four 
small  lamps;  and  T  being  the  result  of  the  combination  of  C 
and  L. 

A  great  opportunity  lies  in  combining  science  and  art  in 
fixtures  for  the  dining  room  which  carry  out  a  definite  aim. 
Silk  shades  on  chandeliers  provide  excellent  opportunities 
especially  in  large  dining  rooms.  At  the  present  time  it  is 
necessary  to  design  a  fixture  and  to  have  it  made  in  order  to 
enjoy  the  greater  possibilities  of  lighting  over  the  dining  table; 
but  doubtless  lighting  units  will  be  developed  to  meet  the  needs 
discussed  in  the  foregoing  paragraphs.  At  least  two  baseboard 
outlets  will  be  welcomed  in  the  average  dining  room;  one  for 
candlesticks  which  commonly  ornament  the  buffet  and  the 
other  for  an  ornamental  lamp  or  for  various  accessories. 

Bed  Chamber. — The  chief  lighting  in  the  chamber  is  for  com- 
pleting the  toilet  at  the  dresser  or  dressing  table.  Two  wall- 
brackets,  one  on  each  side  of  the  dresser,  provide  the  best 


RESIDENCE  LIGHTING  143 

general  solution  of  this  problem.  Light  from  a  central  fixture 
does  not  fill  the  requirements  at  the  dresser  because  the  light 
must  illuminate  the  side  of  the  person  which  is  viewed  in  the 
mirror  and  this  side  is  usually  that  facing  the  wall.  For  this 
reason  wall-brackets  serve  the  purpose  very  well.  Outlets 
should  be  provided  for  decorative  lamps  which  may  be  placed 
on  the  dresser  and  serve  a  purely  utilitarian  purpose  in  the 
absence  of  wall-brackets  but  such  lamps  are  seldom  high  enough 
and  far  enough  outside  the  line  of  vision  to  be  satisfactory  for 
making  the  toilet.  Two  baseboard  outlets  placed  according 
to  the  wall  space  should  be  provided  in  most  chambers.  It  is 
well  to  provide  an  outlet  in  the  center  of  the  ceiling  controlled 
by  a  switch  near  the  entrance  whether  or  not  this  is  intended  for 
use  initially.  A  light-source  of  small  luminous  output  con- 
cealed in  a  dense  inverted  bowl  provides  a  pleasing  illumination 
for  many  occasions  in  the  chamber.  Some  of  the  modern  units 
in  which  silk  shades  may  be  employed  provide  a  decorative 
quality  which  is  welcomed. 

Bathroom. — Perhaps  the  best  solution  of  the  lighting  in  a 
bathroom  is  to  provide  a  bracket  on  each  side  of  the  mirror. 
The  luminous  portions  of  the  units  should  be  about  5  feet  above 
the  floor  because  in  this  position  there  are  no  prominent  shadows 
on  the  face.  The  man  who  shaves  himself  will  appreciate  this 
and  there  are  many  other  reasons  for  such  a  lighting.  A  single 
unit  cannot  serve  the  purpose  of  lighting  the  face  as  well  as  two 
units.  Owing  to  the  fact  that  the  surroundings  in  a  bathroom 
are  usually  highly  reflecting,  glare  is  seldom  experienced  from 
opal  lamps  of  low  luminous  output  even  when  used  without 
shades.  However,  it  is  easy  to  equip  the  brackets  with  small 
shades  or  even  half-shades.  These  brackets  usually  provide 
satisfactory  lighting  for  the  entire  room. 

Den  and  Study. — The  principles  discussed  in  the  lighting  of 
a  living  room  apply  equally  well  to  the  den  and  to  the  study. 
Perhaps  one  purely  utilitarian  portable  lamp  may  be  desired 
in  these  cases  but  the  lighting  of  such  rooms  is  so  much  a 
matter  of  taste  that  it  cannot  be  discussed  further  with  much 
profit.  Portable  lamps  are  exceedingly  adaptable  to  the 
lighting  problems  in  these  rooms. 


144  THE  LIGHTING  ART 

Kitchen. — The  combination  fixture  which  is  so  often  found 
in  kitchens  projecting  downward  from  the  center  of  the  ceil- 
ing is  usually  a  nuisance  and  is  too  low  to  illuminate  the  entire 
room  satisfactorily.  When  the  light-source  is  low  a  person  is 
generally  obliged  to  work  in  his  own  shadow  because  the  various 
work-places,  including  the  stove,  are  usually  located  near  the 
walls.  If  the  kitchen  is  small  an  electrical  lighting-unit  close 
to  the  ceiling  and  in  the  center  is  fairly  satisfactory.  The  gas 
units  which  cannot  be  placed  at  the  ceiling  may  be  located  on 
the  walls  and  electrical  wall-brackets  may  be  used  to  supple- 
ment the  central  unit.  Control  from  wall-switches  is  very 
convenient. 

These  are  the  most  important  aspects  of  residence  lighting, 
although  lighting  units  in  hallways,  closets,  vestibules,  on 
porches,  in  the  basement  and  in  the  attic  must  be  ranked  as 
conveniences  and  real  necessities  in  most  cases.  These  need 
not  be  discussed  because  the  problems  are  not  difficult.  Ceil- 
ing fixtures  will  be  found  most  satisfactory  in  many  of  these 
cases.  The  element  of  taste  is  such  a  factor  in  residence  light- 
ing and  there  are  so  many  variables  that  it  has  been  the  aim 
to  confine  the  discussion  largely  to  general  principles  and  to 
bring  to  the  attention  some  of  the  mistakes  which  are  commonly 
made.  Residence  lighting  is  a  field  which  is  undeveloped  from 
the  broad  viewpoint  of  lighting.  First  the  multitude  must 
be  awakened  from  their  indifferent  attitude  and  taught  to 
appreciate  the  wonderful  potentiality  of  proper  lighting  in  con- 
tributing to  the  welfare  and  happiness  of  mankind. 

In  the  preceding  paragraphs  the  discussion  has  been  confined 
to  general  principles  of  residence  lighting,  but  in  closing,  it 
appears  of  interest  to  suggest  some  of  the  possibilities  in  light- 
ing which  certainly  will  find  wider  application  as  the  pleasures 
from  lighting  effects  become  more  fully  appreciated.  During 
the  construction  of  a  residence  many  novel  applications  of 
lighting  may  be  incorporated  not  only  to  obtain  more  pleasure 
and  variety  in  lighting  but  to  convert  unattractive  nooks  or 
wall-spaces  into  pleasant  places.  For  example,  it  is  not  too 
theatrical  to  set  a  large  decorative  panel  of  opal  glass  in  the 
ceiling  of  a  dining-room  and  to  install  red,  green,  and  blue  lamps 


RESIDENCE  LIGHTING  145 

( 

above  it  in  a  space  which  has  been  painted  with  a  permanent 
white  coating.  If  these  lamps  are  controlled  by  means  of  three 
sliding  rheostats  concealed  in  the  wall  any  desired  tint  and 
intensity  of  light  may  be  obtained.  How  such  a  cortrol  of 
light  may  be  utilized  in  adapting  the  lighting  to  the  spirit 
of  the  occasion  is  left  to  the  imagination  of  the  reader.  The  cold 
tint  of  " moonlight,"  the  warm  glow  of  yellow  light,  and  many 
other  effects  of  various  intensities  may  be  obtained.  Surely 
the  cost  of  such  an  installation  is  not  out  of  proportion  to  the 
enjoyment  of  it  in  the  more  pretentious  residences. 

A  gloomy  hallway  or  alcove  may  be  equipped  with  a  hori- 
zontal lattice  placed  a  foot  or  two  from  the  ceiling  and  upon 
this,  artificial  vines  may  be  entwined.  Small  lamps  in  re- 
flectors may  be  placed  along  the  wall  above  the  lattice  and  the 
light  may  be  directed  to  the  ceiling.  The  color  of  the  sky 
or  the  usual  "moonlight"  color  may  be  obtained  by  using  color- 
screens  over  the  apertures  of  the  reflectors  or  by  painting  the 
ceiling  with  the  desired  color.  This  indirectly  lighted  ceiling 
as  viewed  through  the  vine-covered  lattice  will  appear  like 
the  sky.  The  same  idea  may  be  carried  out  in  a  high  vertical 
window  by  moving  the  window  to  the  outer  portion  of  the  frame 
and  by  covering  it  with  a  stained  cardboard.  Tubular  re- 
flectors may  be  used  inverted  and  uniformity  in  the  bright- 
ness of  the  background  may  be  obtained  by  a  graduated  reflec- 
tion factor  easily  obtained  by  the  use  of  a  black  water-color. 
The  simplest  method  of  obtaining  the  desired  tint  is  usually  to 
color  the  reflecting  surface  which  is  to  be  viewed.  Many 
occasions  in  the  home  may  be  agreeably  lighted  by  means  of 
the  faint  light  from  such  an  artificial  "moonlight"  window. 
Doubtless  there  are  conditions  when  a  warmer  light  of  higher 
intensity  would  be  desired. 

Unique  and  pleasing  effects  may  be  obtained  by  concealing 
light-sources  in  imitation  flower-boxes  hung  on  the  walls  in 
the  sun  room  or  dining  room  and  perhaps  on  the  porch  and 
in  the  living  room.  Many  decorative  spots  of  light  may  be 
obtained  by  concealing  light-sources  in  vases  and  in  other 
appropriate  decorative  objects.  A  jardiniere  on  a  pedestal 
provides  an  excellent  place  in  which  to  conceal  a  reflector  and 


146  THE  LIGHTING  ART 

a  fairly  large  light-source  from  which  a  large  room  may  be 
indirectly  illuminated.  Artificial  vines  may  be  draped  from 
the  jardiniere  very  effectively.  Vases  containing  lighting  units 
may  be  placed  upon  the  mantle,  upon  bookcases,  or  upon  the 
piano  and  from  these  very  pleasing  indirect  illumination  may 
be  obtained.  In  the  sun  room  a  central  indirect  fixture  con- 
sisting of  a  suspended  basket  containing  an  artificial  foliage 
plant  provides  an  appropriate  place  for  concealing  a  light- 
source.  These  are  a  few  suggestions  which  are  worthy  of  more 
extensive  use  and  the  householder  who  awakens  to  the  in- 
numerable possibilities  of  lighting  will  be  agreeably  surprised 
at  the  pleasures  innate  in  lighting  effects  adapted  to  the 
surroundings  and  to  the  various  occasions. 


CHAPTER  XVII 
COMMERCIAL  LIGHTING 

It  has  been  stated  in  foregoing  chapters  that  the  aim  of  this 
volume  is  chiefly  to  discuss  principles  and  to  present  ideas  which 
have  permanent  value  instead  of  tabulating  data  and  presenting 
specifications  which  are  subject  to  more  or  less  change  as  light- 
sources  and  lighting  units  are  developed  and  improved.  The 
engineering  data  pertaining  to  lighting  equipment  may  be  ob- 
tained from  manufacturers  and  dealers  and  these  form  the 
basis  of  much  of  the  literature  on  lighting;  however,  discussions 
of  the  broader  principles  and  of  many  interesting  details  which 
form  the  basis  of  creative  lighting-practice  are  relatively  rare 
and  are  not  readily  accessible  to  a  great  percentage  of  those 
interested  in  lighting.  Fortunately  the  present  aim  makes  it 
possible  to  group  various  aspects  of  lighting-practice  into  a  few 
classes  and  therefore  under  the  title  of  this  chapter  all  kinds  of 
stores  and  show-windows  will  be  discussed  more  or  less  as  a 
whole. 

In  stores  the  laying-out  of  outlets  and  the  determination  of 
the  consumption  of  gas  or  electricity  per  square  foot  of  floor- 
area  for  various  kinds  of  lighting  systems  and  environments  are 
engineering  problems  whose  solutions  have  been  fairly  well 
standardized.  Experience  and  observation  of  other  installa- 
tions make  it  possible  to  choose  satisfactory  lighting  units 
especially  when  a  degree  of  freedom  usually  exists  in  the  choice 
of  lamps  of  a  satisfactory  luminous  output  even  after  the  in- 
stallation of  the  lighting  accessories  has  been  made.  Gross 
errors  in  the  engineering  of  lighting  are  far  rarer  than  failures 
to  recognize  other  pertinent  factors  and  to  utilize  the  advantages 
of  details  which  are  not  commonly  considered  in  an  engineering 
solution  of  the  lighting  problem. 

In  viewing  the  field  of  lighting  broadly  it  is  easy  to  conclude 
that  the  purely  engineering  aspect  of  lighting  has  been  much 

147 


148  THE  LIGHTING  ART 

better  taken  care  of  than  the  artistic,  psychological  and  purely 
scientific  aspects.  The  engineer  has  kept  abreast  of  the  times 
and  much  lighting  progress  is  due  to  his  efforts  but  when  he 
alone  attempts  to  be  responsible  for  utilizing  the  entire  poten- 
tiality of  light  it  is  found  that  much  of  this  is  unused.  It  is 
just  beginning  to  be  recognized  generally  that  there  is  a  vast 
portion  of  lighting  which  is  not  engineering  and  cannot  be  suc- 
cessfully practiced  by  the  engineer  who  has  not  studied  the 
various  other  aspects  of  lighting.  This  criticism  applies  to 
commercial  lighting  as  well  as  to  nearly  all  fields  of  lighting- 
practice. 

The  engineer  may  be  mildly  criticized  for  bringing  into  light- 
ing-practice the  word  "  efficiency "  for  its  usage  has  far  out- 
grown its  intended  purpose  and  has  done  much  to  hamper  the 
utilization  of  the  greater  possibilities  of  light.  Efficiency  is 
an  excellent  slogan  to  apply  judiciously  to  lighting  apparatus 
because  it  is  folly  to  waste  light  before  it  leaves  the  unit  or  by 
permitting  it  to  be  lost  upon  surfaces  which  are  not  of  interest 
or  where  it  is  not  desired.  But  to  apply  the  term  "efficiency" 
to  a  lighting  installation  as  a  whole  by  determining  the  ratio  of 
the  lumens  incident  upon  a  certain  "work-plane"  to  the  total 
lumens  emitted  by  the  light-sources  is  misleading  and  even 
unjustifiable  and  is  in  reality  an  admission  that  only  the 
engineering  aspects  are  being  considered.  It  is  also  mislead- 
ing and  unjustifiable  to  consider  the  efficiency  of  a  lighting 
installation  to  be  the  reciprocal  of  the  cost  of  operating  it.  If 
the  term  must  be  used  let  it  represent,  in  the  broader  sense,  the 
ratio  of  satisfactoriness  to  cost.  It  may  surprise  some  illu- 
minating engineers  to  learn  that  the  merchant  does  not  always 
hold  cost  of  lighting  above  satisfactoriness.  This  has  been 
well  exemplified,  for  example,  in  the  propagation  of  artificial 
daylight  for  commercial  lighting.  Notwithstanding  the  lower 
luminous  efficiency  of  artificial-daylight  units  and  the  other 
factors  tending  to  increase  the  cost  of  such  lighting,  many 
merchants  have  adopted  artificial-daylight  illumination.  This 
is  an  excellent  example  because  no  other  factors  entered  in 
many  cases  except  quality  of  light  and  increased  cost  of  light- 
ing. Increased  satisfactoriness  balanced  increased  cost.  The 


COMMERCIAL  LIGHTING  149 

illuminating  engineer  has  introduced  the  word  " efficiency" 
into  lighting  parlance  but  recognizing  the  deterrent  effect  of  its 
narrow  usage  he  will  do  much  to  alter  its  meaning  when  applied 
to  lighting  as  viewed  broadly.  The  greater  possibilities  of 
lighting  cannot  be  employed  without  reducing  the  efficiency  in 
its  narrow  sense  but  when  these  possibilities  are  realized  the 
efficiency  in  its  broad  meaning  will  be  increased. 

Any  of  the  various  systems  of  lighting  will  doubtless  find 
suitable  places  among  the  extensive  variety  of  stores.  It  ap- 
pears that  the  enclosing  unit  or  the  so-called  semi-indirect  unit 
is  more  generally  satisfactory  for  store-lighting  than  other 
types  of  units  when  both  attractiveness  and  utilization  effi- 
ciency are  considered.  Direct-lighting  fixtures  of  deep  opal 
or  prismatic  shades  appear  to  be  satisfactory  in  many  stores 
especially  when  bowl-frosted  lamps  are  used  or  when  the  light- 
sources  are  shielded  from  view.  Unless  the  fixtures  are  artistic 
it  does  not  appear  that  direct-lighting  fixtures  with  open  shades 
can  contribute  as  much  to  the  attractiveness  of  the  store  as 
enclosing  units.  The  latter  usually  make  it  possible  from  an 
engineering  standpoint  to  use  light-sources  of  high  luminous 
output,  thus  contributing  to  efficiency  as  well  as  to  attractive- 
ness. Some  classes  of  stores,  for  example,  jewelry  stores,  ap- 
pear more  attractive  under  the  glittering  effect  of  many  light- 
sources.  Jewelry  loses  much  of  its  attractive  glitter  under 
highly  diffused  lighting  and  it  is  a  legitimate  use  of  light  to  dis- 
play goods  in  the  best  manner.  In  such  cases  direct-lighting 
units  with  open  pendant  shades  may  be  used  to  screen  the 
sources  from  the  observer.  Incidentally,  the  lighting  of  dia- 
monds and  other  jewels  is  an  important  matter  both  as  to 
quality  and  distribution  of  light.  The  dealer  prefers  to  buy 
such  goods  under  a  light  of  daylight  quality  and  of  a  distribu- 
tion such  as  obtains  from  a  patch  of  sky.  It  is  impossible  to 
judge  a  diamond  with  certainty  under  the  glittering  light  from 
a  myriad  of  yellowish  light-sources. 

As  has  been  stated  it  appears  that  a  fairly  diffused  lighting 
generally  renders  a  store  more  attractive  as  a  whole  and  illu- 
minates shelving  and  various  displays  as  well  as  the  decorative 
features  of  the  interior.  Shadows  are  necessary  for  good  seeing, 


150  THE  LIGHTING  ART 

hence  the  enclosing  unit  or  the  semi-indirect  unit  serves  the 
purpose  very  well.  Besides  the  other  objections  which  have 
been  mentioned  regarding  the  multiple-unit  direct-lighting 
fixture,  the  multiple  shadows  are  sometimes  annoying.  The 
purely  indirect  system  does  not  appear  to  be  generally  applic- 
able to  stores  although  there  are  classes  of  stores  where  it  is 
very  appropriate.  For  example,  a  furniture  store  with  its 
mass  of  large  objects,  many  of  which  have  glossy  surfaces, 
may  be  lighted  satisfactorily  by  indirect  systems. 

The  appearances  of  colors  are  of  primary  importance  in 
nearly  all  stores  and  inasmuch  as  illuminants  are  now  available 
for  general  lighting  which  approximate  daylight  in  spectral 
composition  this  aspect  is  worthy  of  discussion.  In  Chapters 
X  and  XI  artificial  daylight  and  its  applications  have  been  dis- 
cussed but  there  are  certain  points  which  may  be  brought  out 
here.  As  discussed  in  those  chapters  an  illuminant  of  daylight 
quality  is  the  logical  illuminant  for  viewing  colors  and  the 
daylight  appearance  of  nearly  all  objects  is  the  one  on  which 
judgments  will  usually  be  based.  Of  course  in  the  case  of  an 
evening  gown  which  is  to  be  worn  only  under  artificial  light 
its  appearance  under  this  illuminant  is  of  chief  interest;  how- 
ever, curiosity  usually  leads  to  a  desire  to  view  even  such  a  gown 
under  daylight.  No  one  would  think  of  forming  a  judgment  of 
a  colored  object  under  a  red  illuminant  in  which  only  the  yellow, 
orange,  and  red  rays  existed.  In  a  rough  manner  ordinary 
artificial  light  commonly  used  in  stores  may  be  considered  to 
lie  between  this  red  illuminant  and  daylight  in  quality  because 
in  it  the  yellow,  orange,  and  red  rays  are  abundant  and  the 
violet  and  blue  rays  are  relatively  rare.  The  quality  of  ordinary 
artificial  light  is  purely  accidental  and  has  little  value  as  an 
illuminant  for  color-discrimination  except  on  the  basis  that  the 
objects  which  are  purchased  under  it  are  to  be  viewed  under  it. 
Not  only  has  our  judgment  of  color  developed  under  daylight 
illumination  and  our  color-sense  evolved  amid  the  environ- 
ment of  daylight  but  we  still  remain  " daylight"  individuals 
to  a  dominating  degree.  In  fact,  it  may  be  said  lhat  daylight 
is  a  part  of  the  scheme  of  creation.  For  these  reasons  artificial 
daylight  finds  a  field  in  commercial  lighting. 


COMMERCIAL  LIGHTING  151 

In  order  to  be  able  to  deal  definitely  with  the  problems  of 
color  the  lighting  specialist  should  be  acquainted  with  the  chief 
principles  of  the  science  and  art  of  color.  One  of  the  most  an- 
noying conditions  for  discriminating  colors  is  that  found  in 
many  stores  where  daylight  and  artificial  light  intermingle 
though  coming  from  different  directions.  For  example,  if  a 
piece  of  colored  goods,  especially  a  glossy  silk,  be  examined 
under  the  downward  light  from  an  ai  tificial  lighting  unit  and 
at  the  same  time  daylight  is  arriving  in  a  horizontal  direction 
or  nearly  so,  it  is  difficult  to  form  a  conception  of  the  color  of 
the  goods.  Such  an  experiment  is  convincing  to  a  merchant. 
Means  for  helping  to  overcome  any  objection  due  to  the  cold- 
ness of  artificial  daylight  have  already  been  discussed.  This 
objection  is  a  result  of  prejudice  or  habit  and  it  is  not  difficult  to 
overcome  both  by  the  presentation  of  facts  and  by  resorting 
to  illusions.  It  should  also  be  remembered  that  stores  are 
frequented  chiefly  in  the  daytime  and  if  it  is  lighted  by  artificial 
daylight  it  will  not  be  considered  cold  in  appearance  by  the 
average  customer,  but  will  be  unconsciously  considered  to  be 
illuminated  most  delightfully  by  an  abundance  of  daylight. 
This  is  the  psychological  effect  on  many  customers  as  deter- 
mined by  actual  investigation.  Care  should  be  taken  to  avoid 
the  use  of  yellowish  tints  and  shades  too  predominantly  on  the 
ceiling  if  much  light  is  reflected  from  it  to  the  workplane  be- 
cause this  light  would  be  colored  by  selective  reflection.  This 
alteration  may  be  sufficient  to  change  the  artificial  daylight 
materially  toward  the  ordinary  yellowish  artificial  light.  For 
accurate  color-matching,  various  artificial-daylight  units  are 
available  which  may  be  placed  above  counters  or  in  rooms 
especially  designed  for  the  purpose.  Some  stores  have  been 
equipped  with  rooms  side  by  side  lighted  by  ordinary  artificial 
illuminants  and  by  artificial  daylight  respectively.  These  are 
used  for  viewing  gowns,  furs,  cloaks,  etc. 

In  one  instance,  at  least,  a  store  has  been  provided  with  a 
room  containing  foot-lights  and  border-lights  equipped  with 
movable  color-screens  for  the  purpose  of  viewing  theatrical 
costumes. 

Many  special  distributions  of  light  are  applicable  to  specific 
11 


152  THE  LIGHTING  ART 

cases  in  stores.  For  example,  rug-racks  have  been  lighted  by 
means  of  borders  of  lamps  in  reflectors.  In  one  case  a  merchant 
was  found  to  be  displaying  rugs  under  amber  lamps  which  made 
the  rugs  appear  somewhat  faded  and  oriental-like  but  the  ille- 
gitimacy of  such  a  procedure  is  obvious.  Nearly  everyone  can 
recall  instances  when  a  rug  or  other  colored  object  which  had 
been  selected  under  artificial  light  in  the  store  has  presented 
quite  a  different  appearance  under  daylight  illumination  in  the 
home.  Similarly  such  objects  often  appear  widely  different 
in  the  home  in  the  daytime  or  at  night.  These  are  practical 
examples  of  the  importance  of  quality  of  light  in  the  selection 
of  colored  objects. 

The  problem  of  show-case  lighting  is  largely  one  of  engineer- 
ing, that  is,  in  the  design  of  small  reflectors  and  in  obtaining 
light-sources  of  sufficiently  low  luminous  output  for  illuminat- 
ing the  small  areas  in  show-cases.  Various  excellent  reflectors 
are  available  but  the  chief  difficulty  is  encountered  in  obtaining 
modern  light-sources  of  small  enough  wattage  which  have  the 
desired  color-value.  In  stores  illuminated  by  artificial  day- 
light sometimes  an  attractive  effect  is  obtained  by  lighting  the 
cases  with  ordinary  illuminants,  the  warm  tone  being  an  at- 
tractive contrast  with  the  general  lighting.  The  general  prin- 
ciples of  show-case  lighting  are  similar  to  those  of  show-win- 
dows but  the  possibilities  in  the  latter  are  much  greater. 

The  engineering  principles  of  lighting  show-windows  are 
largely  a  matter  of  directing  the  light  downward  and  toward  the 
rear  of  the  window.  The  selection  of  the  type  of  reflector 
depends  upon  the  relative  dimensions  of  the  window.  For  a 
high  shallow  window  it  is  obvious  that  a  more  concentrating 
reflector  is  necessary  than  for  a  low  deep  window.  Engineer- 
ing data  and  rules  are  obtainable  from  manufacturers  of  light- 
ing equipment  so  space  need  not  be  given  to  a  discussion  of 
this  aspect.  The  units  are  logically  placed  along  the  upper 
front  border  of  the  window  and  are  shielded  either  by  a  per- 
manent opaque  portion  of  the  front  or  by  means  of  a  valance 
but  various  other  arrangements  of  light-sources  are  also  in  use. 

The  primary  object  of  a  show-window  is  to  attract  attention 
and  to  display  goods.  In  many  respects  it  may  be  considered 


COMMERCIAL  LIGHTING  153 

to  be  similar  to  a  stage  and  hence  it  should  be  highly  illumi- 
nated as  compared  with  the  exterior  surroundings.  For  this 
reason  there  can  be  no  fixed  standard  of  illumination  intensity. 
A  show-window  on  a  "white-way"  street  should  be  illuminated 
much  more  intensely  than  one  on  a  relatively  dark  side  street. 
The  light-sources  should  be  concealed  and  the  whole  effect 
should  simulate  a  stage-setting.  Incidentally  those  numerous 
show-windows  in  which  glaring  light-sources  greet  the  observer, 
unwittingly  simulate  the  " glare"  lights  which  are  sometimes 
used  to  blind  the  audience  in  a  theatre  when  a  quick  change  of 
setting  is  made  without  lowering  the  curtain.  The  observer 
sees  the  display  unsatisfactorily  if  he  possesses  the  courage  to 
withstand  the  glare  of  such  exposed  light-sources  so  common  in 
the  lower  grade  show-windows. 

Show-windows  may  be  provided  with  top-lights,  foot-lights, 
and  side-lights  depending  upon  taste  and  requirements.  The 
top-lights  are  indispensable  for  most  show-windows.  The  foot- 
lights may  be  criticised  from  the  viewpoint  of  unnatural  di- 
rection of  dominant  light  although  they  are  of  advantage  in 
providing  a  diffused  light  for  illuminating  the  shadows.  In 
many  cases  the  theatrical  effects  obtainable  from  them  justify 
their  use.  Side-lights,  if  they  can  be  successfully  concealed, 
also  provide  additional  possibilities  in  lighting.  Corner- 
windows  present  some  difficulties  in  concealing  the  border 
units  but  deep  reflectors  have  eliminated  this  difficulty  to 
some  extent.  In  some  cases  stationary  vertical  louvers  have 
been  installed  between  the  units  with  excellent  success.  It  is 
not  unusual  in  show-windows  of  high-grade  department  and 
dry-goods  stores  to  provide  several  circuits  and  movable  color- 
screens;  and  rheostatic  control  for  the  purpose  of  obtaining 
beautiful  color-effects  may  be  used  advantageously.  Base- 
board and  floor  outlets  are  convenient  for  obtaining  special 
effects  from  portable  lamps.  Some  use  has  been  made  of 
pendant  fixtures  in  the  show-window,  including  all  kinds  from 
direct  to  indirect  and  many  windows  are  lighted  through 
ceiling  skylights.  These  methods  are  appropriate  with  some 
settings  but  the  general  case  is  solved  best  by  upper  border- 
units  near  the  front  of  the  window. 


154  THE  LIGHTING  ART 

The  background  in  show-windows  is  important  from  the 
viewpoint  of  good  lighting  conditions  and  of  general  psycho- 
logical effects.  It  should  be  of  a  dull  finish  otherwise  it  will  act 
like  a  mirror  and  reflect  images  of  the  light-sources  toward  the 
observer.  Many  beautifiul  show-windows  with  glossy  back- 
grounds are  robbed  of  some  of  their  artistic  value  by  the  reflec- 
tion of  images  of  the  light-sources.  The  color  of  the  light  in- 
fluences the  color  of  the  goods  and  besides  the  spectacular  and 
artistic  uses  of  colored  light,  artificial  daylight  is  used  quite 
extensively  in  show-windows.  The  considerations  are  quite 
the  same  as  in  using  artificial  daylight  in  the  store;  however, 
the  psychological  effect  of  a  background  of  warm  colors  may 
be  advantageously  employed.  Most  of  the  light  on  the  goods 
is  directed  toward  them  by  the  reflectors  and  the  goods  ordi- 
narily occupy  but  a  portion  of  the  entire  show-window  scene. 
If  a  warm  background  is  employed  the  goods  are  still  lighted 
with  nearly  the  same  daylight  quality  though  the  whole  scene 
is  considerably  "warmer"  owing  to  the  psychological  effect  of 
the  large  area  of  background.  Of  course  some  light  is  altered 
in  color  and  finds  its  way  to  the  goods  but  this  sacrifice  can  be 
made  if  necessary  in  order  to  have  light  of  a  fair  daylight  quality 
on  the  goods  and  yet  retain  at  night  the  attractive  warmth  of 
the  scene  as  a  whole.  Such  backgrounds  are  easily  obtained  by 
the  use  of  draperies  of  deep  shades  of  the  desired  color. 

The  show-window  is  often  unsatisfactory  in  the  daytime 
owing  to  the  images  of  external  objects  reflected  from  the  plate 
glass.  An  attempt  has  been  made  to  avoid  this  difficulty  by 
using  a  concave  glass  as  viewed  from  the  exterior.  This  is 
not  completely  successful  because  regardless  of  the  orientation 
of  the  glass  there  is  usually  a  bright  reflected  image  which 
reaches  the  eyes.  Attempts  have  been  made  to  increase  the 
intensity  of  daylight  illumination  in  the  window  by  the  use 
of  prism  glass  in  the  ceiling  and  in  the  front  above  the  window. 
These  may  possibly  aid  in  reducing  the  prominence  of  the  images 
reflected  from  the  glass  through  an  increased  intensity  of  illu- 
mination inside  the  window  but  ordinarily  they  do  not  do  this 
to  an  appreciable  extent.  Such  prism  glasses  are  valuable  aids 
in  the  lighting  of  show-windows  in  special  cases.  Awnings 


COMMERCIAL  LIGHTING  155 

appear  to  be  the  most  practicable  means  of  reducing  the  annoy- 
ance due  to  reflected  images  but  these  cannot  prevent  the  reflec- 
tion of  the  image  of  the  bright  sidewalk.  There  appears  to  be 
no  practical  method  of  overcoming  these  difficulties  in  the 
show-window  which  directly  faces  the  street  as  long  as  the 
exterior  objects  are  bright  but  the  awning  greatly  reduces  the 
annoyance  of  reflected  images  if  it  is  not  too  bright,  that  is, 
if  not  too  highly  transmitting. 

In  show-window  lighting  many  of  the  possibilities  in  the  dis- 
tribution of  light,  shade,  and  color  may  be  applied.  Relative 
dark  backgrounds  provide  striking  contrasts  with  the  objects 
which  are  displayed  and  on  the  other  hand,  backgrounds  of 
relatively  high  reflection-factor  lend  an  airiness  to  the  picture 
which  is  very  charming  for  certain  settings.  Sometimes  a  single 
object  in  a  window  amid  unglazed  or  velvety  surroundings 
provides  an  extremely  attractive  display  especially  if  this  object 
is  strikingly  illuminated.  Shadows  are  necessary  on  objects  for 
it  is  largely  the  modulation  from  high-light  to  shadow  which 
models  the  objects.  Even  the  nuances  of  light  and  shade  on  a 
draped  silk  fabric  provide  a  more  artistic  picture  than  the  uni- 
formity and  flattened  effect  of  highly  diffused  lighting.  Foot- 
lights have  value  in  controlling  the  intensity  of  the  shadows 
which  are  due  to  the  directed  light  from  the  upper  border- 
lights.  A  fact  gleaned  from  the  study  of  light  and  shade  is 
that  vertical  and  symmetrical  shadows  are  not  generally  as 
artistic  as  oblique  and  asymmetrical  shadows.  However,  under 
the  uniform  spacing  of  border-lights  asymmetrical  distribution 
of  light  cannot  be  obtained.  An  ideal  arrangement  of  outlets 
for  the  show-window  is  to  have  these  spaced  entirely  around  the 
four  sides  of  the  vertical  front  of  the  window  and  to  have  the 
lamps  concealed.  By  means  of  such  an  arrangement  the  lamps 
need  not  be  uniformly  spaced  but  may  be  shifted  into  various 
sockets  in  order  to  obtain  the  desired  dominant  direction  of 
light.  For  artistic  effects  the  lighting  in  a  show-window  does 
not  need  to  be  uniform  for  all  settings.  Outlets  should  be  pro- 
vided generously  and  in  order  to  be  prepared  for  special  effects 
as  many  as  three  intermingled  circuits  may  be  provided.  These 
may  be  equipped  with  color-screens  and  controlled  by  means  of 


156  THE  LIGHTING  ART 

motor-driven  rheostats  in  order  to  obtain  attractive  mobile- 
color  effects. 

The  lighting  accessories  which  are  available  for  show-window 
lighting  are  trough  reflectors  usually  with  silver  reflecting 
surfaces;  enameled,  aluminized,  and  silvered  opaque  reflectors; 
prismatic  and  opal% glass  reflectors;  portable  lamps  and  various 
types  of  ornamental  fixtures.  In  general,  the  silvered  and 
prismatic  reflectors  for  single  light-sources  are  the  most  satis- 
factory for  concealed  border-lights  at  the  top  of  the  window 
although  the  accessory  should  be  selected  to  meet  the  conditions. 
Data  as  to  distribution,  spacing,  etc.,  are  readily  obtainable 
from  manufacturers. 

The  applications  of  lighting  need  not  be  confined  to  that  of 
ordinary  practice;  in  fact,  the  greater  possibilities  are  found  in 
utilizing  lighting  effects  more  nearly  approaching  those  of  the 
stage.  That  lighting  can  be  made  to  provide  striking  and 
attractive  effects  quite  appropriate  to  the  display  will  be  shown 
by  discussing  a  possibility.  Let  us  assume  an  ordinary  window 
in  a  large  department  store  but  a  double  casement  window 
(without  glazing)  will  be  supposed  to  be  provided  in  the  center 
of  the  background  of  the  window.  Four  feet  behind  the  rear 
of  the  window  another  partition  may  be  erected  and  upon  this 
any  scene  painted  on  canvas  may  be  supported.  This  scene 
may  be  illuminated  by  means  of  border-lights  concealed  behind 
the  first  wall  or  the  background  of  the  window.  By  means  of 
tinted  lamps  this  scene  may  be  lighted  just  as  it  would  be  on 
the  stage  and,  if  desired,  mobile-color  effects  may  be  obtained 
by  means  of  motor-driven  rheostats.  Let  us  suppose,  for 
example,  that  winter  furs  are  being  displayed  as  is  usually  the 
case  during  the  hot  days  of  autumn.  Surely  the  psychological 
effect  of  lighting  may  be  used  to  advantage  in  order  to  interest 
purchasers  of  furs  when  the  weather  does  not  emphasize  their 
necessity.  With  this  preparation  the  scene  may  be  set  in 
the  following  manner.  The  window  may  be  furnished  as  an 
interior  room  lighted  by  means  of  a  floor-lamp  and  a  very  dim 
diffused  light  from  the  border-lights.  The  figure  of  a  woman  is 
standing  gazing  out  of  the  open  window  at  a  snowy  mountainous 
landscape  lighted  by  means  of  lamps  tinted  a  blue-green.  She 


COMMERCIAL  LIGHTING  157 

wears  a  fur  cloak  thrown  open  but  muff  and  stole  lie  carelessly 
upon  the  library  table.  To  carry  out  the  idea  of  a  fur  display, 
fur  rugs  may  be  used  on  the  floor.  Lighting  is  the  principle 
factor  in  the  effect  of  this  scene.  The  warm  glow  of  the  interior 
is  contrasted  with  the  coldly-lighted  snowy  scene  and  by  sug- 
gestion such  a  setting  would  surely  awaken  more  interest  in 
furs  in  August  or  September  than  a  display  which  is  illuminated 
in  the  ordinary  manner.  Similarly  as  goods  are  commonly 
displayed  out  of  season  the  latter  may  be  vividly  brought  to 
mind  *by  means  of  the  appropriate  setting  and  lighting.  In- 
numerable possibilities  in  lighting  await  the  show-window 
expert  who  comes  to  the  realization  that  the  window  is  a  stage, 
and  should  be  provided  with  the  simple  equipment  which  makes 
it  possible  to  display  goods  and  to  attract  attention  by  utiliz- 
ing all  of  the  potentiality  possessed  by  distributions  of  light, 
shade,  and  color. 


CHAPTER  XVIII 
LIGHTING  IN  PUBLIC  BUILDINGS 

Those  who  are  entrusted  with  the  lighting  of  public  build- 
ings have  a  civic  duty  to  perform  in  safeguarding  vision  and 
life.  In  the  case  of  a  decorative  interior  there  is  a  further  re- 
sponsibility in  revealing  the  beauty  of  the  interior  by  combining 
science  and  art  in  lighting.  In  the  schools  of  this  country 
twenty  million  pairs  of  eyes,  immature  in  growth  and  in  func- 
tion, are  daily  being  subjected  to  the  strain  of  close  work. 
Many  museums  are  filled  with  art  treasures  and  objects  of 
historical  interest  and  to  display  these  properly  the  lighting 
must  be  well  done.  In  the  theatre  and  in  other  auditoriums 
where  audiences  gather  it  is  a  duty  to  safeguard  lives  and  in 
this  respect  ordinary  and  emergency  lighting  systems  are  im- 
portant factors.  In  many  beautiful  interiors  of  public  build- 
ings the  lighting  is  not  doing  its  part  though  there  are  relatively 
few  who  feel  capable  of  criticizing  and  often  there  is  no  definite 
place  to  submit  a  complaint.  In  general,  the  public  goes  about 
its  business  and  the  unsatisfactory  condition  remains.  The 
architect  should  avoid  such  mistakes  by  soliciting  the  aid  of 
the  lighting  specialist.  As  an  example  of  the  foregoing  a  public 
building  may  be  cited  in  which  a  few  large  mural  paintings 
decorate  the  walls.  The  initial  cost  of  these  paintings  was 
nearly  one  hundred  thousand  dollars,  but  largely  due  to  the 
character  of  lighting  systems,  these  paintings  cannot  be  satis- 
factorily viewed.  In  this  chapter  the  lighting  of  a  few  classes 
of  public  buildings  will  be  discussed  briefly.  The  relation  of 
lighting  and  architecture  will  only  be  touched  upon  as  in  other 
chapters  because  this  subject  is  treated  separately  in  Chapter 
XIV. 

Schools. — The  eyes  of  school  children  are  immature  in  growth 
and,  therefore,  are  subject  to  permanent  disorder  through  mis- 
use. Nearsightedness  is  a  common  defect  caused  by  maintain- 
ing the  eyes  in  a  position  too  close  to  the  work  as  is  necessary 

158 


LIGHTING  IN  PUBLIC  BUILDINGS  159 

under  bad  lighting  conditions.  Records  show  that  the  per- 
centage of  school  children  possessing  defective  vision  increases 
with  their  age  under  improper  lighting  and  decreases  under 
proper  lighting.  The  lighting  specialist  should  view  his  prob- 
lem from  the  broad  aspect  which  includes  vision  and  the  ap- 
pearances of  objects  or  of  settings  as  a  whole.  In  the  school- 
room the  problem  of  safeguarding  vision  does  not  end  with  the 
spacing  and  design  of  the  lighting  units,  for  it  involves  the 
character  of  the  surroundings  and  other  factors.  Daylight  is 
usually  of  greater  importance  in  schools  than  artificial  light 
but  the  latter  is  becoming  more  and  more  necessary  especially 
in  city  schools.  The  daylighting  of  schoolrooms  is  being  done 
fairly  well  at  the  present  time  because  it  has  been  extensively 
studied  by  architects  and  engineers.  For  sanitary  reasons  it 
should  be  possible  for  sunlight  to  penetrate  as  many  rooms  as 
possible,  although  the  windows  should  be  equipped  with  dif- 
fusing shades  for  controlling  the  daylight  while  the  rooms  are 
occupied.  The  most  approved  shade  is  a  double  roller  at  the 
meeting  rail  of  the  double  window  so  that  one  shade  may  be 
pulled  upward  and  the  other  downward. 

There  is  still  some  question  whether  or  not  a  classroom  should 
have  windows  only  on  the  side  to  the  left  of  the  pupils  or  on  the 
rear  side  as  well.  However,  unilateral  lighting  appears  to  be 
satisfactory  for  rooms  less  than  20  feet  in  width.  The  window- 
area  should  not  be  less  than  20  per  cent,  of  the  floor-area  and 
the  width  of  the  room  should  not  be  greater  than  twice  the 
height  of  the  top  of  the  window. 

The  light-value  of  a  window  depends  upon  the  brightness 
of  the  sky,  the  amount  of  sky  visible  at  a  given  point,  and  in- 
directly upon  the  reflection-factors  of  the  surroundings  and 
upon  the  dimensions  of  the  room.  The  upper  part  of  the 
window  is  more  effective  in  lighting  the  interior  than  the 
lower  part  so  that  the  window  area  should  extend  close  to  the 
ceiling.  Observations  in  well-lighted  rooms  show  that  under 
average  conditions  of  daylight,  satisfactory  illumination  is 
usually  obtained  when  the  visible  sky %  subtends  a  minimum 
vertical  angle  of  5  degrees  at  any  work-point.  In  cases  where 
the  horizon  is  obstructed  the  window-area  should  be  larger 


160  THE  LIGHTING  ART 

than  the  minimum  recommended  and  prismatic  glass  may  be 
utilized  for  directing  the  light  into  the  room.  Light-courts 
should  have  high  reflection-factors.  The  light- value  of  a 
window  may  be  determined  at  a  given  point  by  multiplying 
the  area  of  the  window  through  which  sky  is  visible  by  the  sky- 
brightness  and  dividing  by  the  square  of  the  distance  from  the 
window  to  the  point  of  interest.  This  gives  the  minimum 
value  of  illumination  at  this  point  because  some  light  is  con- 
tributed by  reflection  from  various  surfaces.  This  inverse 
square  law  does  not  hold  unless  the  distance  is  several  times  the 
maximum  dimension  of  the  apparent  source.  The  bright- 
ness of  a  clear  sky  may  be  taken  as  i  lambert  or  the  approxi- 
mate equivalent  of  2  candles  per  square  inch.  Large  rooms 
dependent  upon  natural  light  should  have  light  on  two  sides 
preferably  on  the  left  side  and  on  the  rear  of  pupils  as  seated. 
In  schoolrooms,  general  lighting  should  be  adopted  in  all 
cases.  When  the  ceilings  are  high,  direct-lighting  may  be  satis- 
factory if  the  shades  are  deep  and  highly  diffusing.  Maximum 
brightnesses  and  brightness  contrasts  should  be  kept  as  low 
as  possible  and  should  not  exceed  those  recommended  on  page 
33.  Semi-indirect  lighting  by  means  of  units  equipped  with 
dense  opal  glass  is  generally  the  most  approved  system  for 
ordinary  classrooms  of  small  and  medium  sizes.  In  large  class- 
rooms, auditoriums,  etc.  the  best  solution  is  often  found  in 
lighting  from  concealed  sources  or  by  indirect  systems.  Local- 
ized lighting  by  means  of  units  placed  on  desks,  tables,  and 
work-benches  or  hung  near  machines  is  generally  condemned. 
In  special  cases  such  a  system  is  satisfactory  if  the  light-sources 
are  well-shaded  and  the  units  are  fixed  in  an  unalterable 
position.  However,  there  appear  to  be  few  cases  where 
general  lighting  is  not  justifiable  from  the  standpoints  of 
safety  and  of  better  lighting.  The  illumination  on  the  plane 
of  the  desk-tops  and  on  other  work-planes  should  be  as  uni- 
form as  is  practicable.  This  is  obtained  by  a  generous  dis- 
tribution of  outlets.  If  there  is  a  definite  directedness  to  the 
light  this  component  should  fall  from  the  left  of  the  pupil 
(assuming  general  right-handedness)  in  order  that  the  shadow 
of  the  hand  will  not  be  annoying  in  writing. 


LIGHTING  IN  PUBLIC  BUILDINGS  161 

Glossy  surfaces  of  paper,  woodwork,  desk-tops,  walls  and 
blackboards  are  likely  to  cause  eyestrain  because  of  the  specular 
reflection  of  images  of  the  light-sources,  therefore  dull  surfaces 
are  recommended.  Blackboards  should  be  placed  in  such 
positions  that  no  images  of  light-sources  will  be  reflected 
toward  the  pupils.  Simple  laws  of  reflection  may  be  applied  in 
order  to  determine  a  correct  position  for  a  blackboard.  In 
cases  in  which  glare  of  this  sort  cannot  be  otherwise  avoided  it 
is  well  to  provide  auxiliary  illumination  from  local  artificial 
light-sources  properly  screened  from  the  pupils.  The  black- 
board area  should  be  the  minimum  which  may  be  required. 

Proper  distribution  of  illumination  and  brightness  greatly 
dominates  in  importance  over  quality  of  light  and  distribution 
of  color  in  schoolrooms;  however,  the  latter  are  of  importance. 
The  more  restful  colors  such  as  cream,  shades  of  buff  and  olive 
green  should  be  used  on  the  larger  areas.  In  certain  activities 
artificial  daylight  is  being  successfully  used.  Botany  classes 
at  night  are  better  conducted  under  artificial  sunlight  and  this 
quality  of  light  is  also  in  use  in  art  rooms,  sewing  rooms,  print 
shops,  and  in  laboratories  devoted  to  chemistry  and  domestic 
science. 

Museums. — The  problems  of  lighting  in  museums  varies 
with  the  character  of  the  exhibits  and  the  dimensions  and 
construction  of  the  rooms.  In  a  large  museum  the  lighting 
specialist  finds  a  variety  of  interesting  problems  and  the 
potentiality  of  lighting  should  be  drawn  upon  to  the  fullest 
extent  in  order  to  illuminate  the  objects  properly,  for  their 
value  should  be  due  to  their  appearance  more  than  in  the  mere 
possession  of  them.  This  entire  field  is  open  to  the  lighting- 
artist  as  well  as  many  other  phases  of  lighting.  In  order  to 
bring  out  the  chief  principles  in  the  lighting  of  museums,  a 
few  different  types  of  exhibits  and  rooms  will  be  considered. 
However,  the  problem  of  quality  of  light  may  be  discussed  in 
general  before  taking  up  specific  cases. 

It  cannot  be  denied  that  daylight  is  generally  the  proper 
quality  of  light  for  the  illumination  of  objects  which  are 
exhibited  in  museums  and  therefore  artificial  daylight  should 
be  widely  adopted  in  such  places.  This  has  been  done  in  a 


162  THE  LIGHTING  ART 

number  of  museums  with  exceedingly  satisfactory  results. 
However,  there  arises  the  question  of  the  best  quality  of  day- 
light for  museums.  Northern  exposure  is  desired  by  many 
but  southern  exposure  appears  to  be  preferred  by  a  still  greater 
percentage  of  persons  who  have  given  the  matter  consideration. 
In  such  considerations,  however,  quality  of  light  has  not  been 
the  only  factor,  for  constancy  has  also  been  of  some  weight. 
After  a  prolonged  study  of  this  mal  ter  it  appears,  when  a  judg- 
ment is  rendered  on  quality  alone,  that  the  quality  of  light 
entering  skylights  and  windows  of  southern  exposure  in  this 
hemisphere  is  preferred  by  a  large  majority  of  artists  and  others 
qualified  to  render  an  authoritative  opinion.  For  this  reason 
it  is  legitimate  to  warm  up  the  light  which  enters  north  windows 
by  means  of  light  tints  of  yellow  in  the  curtains  or  draperies 
which  cover  the  windows. 

This  is  a  fortunate  condition  for,  owing  to  the  demands  of 
economy,  the  more  practicable  artificial-daylight  units  which 
are  available  for  general  lighting  more  nearly  simulate  the 
quality  of  light  from  the  sun  than  from  the  north  sky  although 
this  quality  of  daylight  renders  colors  quite  satisfactorily. 
Even  in  the  daytime  an  art  museum  with  neutral  walls  may  be 
rather  cheerless  so  that  the  wall-coverings  best  suited  to  such 
interiors  should  generally  be  a  warm  gray.  Backgrounds  of 
vivid  colors  are  improper  for  exhibits  of  most  works  of  art  if 
the  appearance  of  the  latter  is  primarily  considered,  because  the 
appearance  of  an  object  is  affected  by  its  environment.  For 
example,  a  white  surface  viewed  against  a  pink  background 
appears  of  a  greenish  hue  and  all  colors  are  affected  by  the  color 
and  brightness  of  the  surroundings.  The  gilded  frames  and  the 
warm  gray  backgrounds  also  tend  to  produce  a  more  cheerful 
interior  under  the  illumination  from  artificial-daylight  units. 

In  the  lighting  of  paintings  galleries  there  are  other  funda- 
mental desiderata  besides  daylight  quality  of  light;  namely, 
that  the  brightness  of  the  floor  and  ceiling  should  not  be  too 
great  in  comparison  to  the  walls;  that  the  component  of  light 
vertically  downward  should  not  be  large  in  comparison  with 
that  directed  toward  the  space  on  the  walls  upon  which  pic- 
tures are  to  be  hung;  and  that  there  should  be  no  images  of 


LIGHTING  IN  PUBLIC  BUILDINGS 


163 


bright  light-sources  or  of  other  areas  reflected  from  glazed  or 
varnished  pictures  directly  into  the  eyes  of  an  observer  at  a 
reasonable  viewing  distance.  The  brightness  of  the  floor  may 
be  reduced  to  the  proper  value  by  reducing  its  reflection-factor 
or  by  employing  coverings  of  low  reflection-factor.  Unless 
the  ceiling  is  of  glass  the  same  expedient  may  be  applied  to  it 
but  in  the  case  of  glass  it  is  necessary  to  employ  one  which  is 
not  too  diffusing  in  order  that  it  may  not  become  a  secondary 


/   /__!-*:_ 


tort 


FIG.  38. — Some  principles  applied  to  a  paintings  gallery. 


source  of  a  brightness  greater  than  that  desired.  The  proper 
glass  is  of  great  importance  because  it  must  also  serve  the  pur- 
pose of  obscuring  the  attic  structure.  Rough  refractive  glasses 
appear  to  be  the  most  suitable. 

In  order  to  ascertain  the  conditions  which  will  not  result  in 
annoying  images  reflected  into  the  eyes  of  the  observer,  the 
simple  law  of  reflection,  a,  Fig.  12,  may  be  applied.  If  the 
opposite  walls  and  ceiling  are  bright  and  if  the  latter  is  too  ex- 
tended, there  is  no  escape  in  a  room  of  ordinary  dimensions, 
from  annoying  images  reflected  from  glazed  pictures.  This  is 
shown  diagrammatically  in  Fig.  38  in  which  the  dimensions  are 


164 


THE  LIGHTING  ART 


satisfactory  for  avoiding  this  difficulty.  The  eye-level  may  be 
taken  as  5  feet  above  the  floor  and  the  maximum  height  of  any 
portion  of  a  picture  as  10  feet.  If  the  ceiling  is  high  and  not  too 
extensive  it  will  be  found  that  the  image  of  the  farthest  point  of 


FIG.  39. — Illustrating  some  principles  of  light-control  applied  in  the  Cleveland 

Museum  of  Art. 

the  sub-skylight  glass  will  not  be  reflected  into  the  eyes  of  an 
observer  unless  he  is  close  to  the  picture.  If  the  ceiling  is  low 
or  too  extensive  an  opaque  curtain  may  be  hung  from  the 
ceiling  as  C  (or  several  if  necessary  at  different  points  on  the 
ceiling)  in  order  to  eliminate  this  difficulty.  The  use  of  an 
opaque  or  dense  diffusing  velum  V  is  also  an  effective  expedient. 
HoweVer,  these  are  usually  makeshifts  which  are  unsightly. 


LIGHTING  IN  PUBLIC  BUILDINGS  165 

The  velum  possesses  the  desirable  feature  of  reducing  the 
downward  component  and  this  idea  may  be  effectually  woven 
into  the  architectural  scheme  of  a  gallery  although  it  has  rarely 
been  done. 

The  reduction  of  the  vertically  downward  component  in 
galleries  which  is  so  tiring  to  the  eyes  may  be  accomplished  by 
using  clerestory  windows  instead  of  a  horizontal  sky-light  and 
by  means  of  louvers  in  the  case  of  roof  and  sub-skylights. 
They  may  be  placed  in  various  positions  depending  upon  the 
conditions.  In  Fig.  39  is  shown  an  application  of  adjustable 
metal  louvers  close  to  the  roof  skylight  in  the  Cleveland 
Museum  of  Art.  By  means  of  these  the  illumination  on  north 
and  south  walls  may  be  equalized  and  the  vertically  downward 
component  may  be  reduced  considerably  in  comparison  with 
that  which  is  directed  toward  the  wall-space  on  which  pictures 
are  hung.  The  artificial-daylight  units  were  placed  as  shown 
in  this  museum  and  the  light  was  directed  toward  the  walls  by 
means  of  projectors.  A  difficulty  in  artificial  lighting  usually 
is  encountered  in  concealing  the  units  or  in  devising  artistic 
units  which  direct  the  light  toward  the  walls.  It  does  not 
appear  that  the  limit  of  ingenuity  has  been  reached  in  the  design 
of  chandeliers  or  of  other  units  which  may  beautify  a  gallery 
and  at  the  same  time  direct  light  toward  the  walls.  Low 
vertical  windows  are  not  justifiable  in  paintings  galleries  owing 
to  the  sacrifice  of  wall-space  and  to  the  unavoidable  reflection 
of  images  of  bright  objects  and  of  the  sky  from  many  of  the 
paintings  directly  into  the  eye.  There  are  many  other  details 
in  the  lighting  of  paintings  galleries  which  become  apparent 
after  due  consideration  of  the  conditions  in  a  specific  case. 

In  sculpture  galleries  the  problem  of  lighting  is  quite  different 
from  the  preceding  one.  The  chief  defects  in  the  lighting  of 
sculpture  galleries  are  found  in  the  multiple  shadows  due  to 
several  light-sources — either  windows  or  artificial  units — and 
the  flattening  effect  due  to  the  diffused  light  from  an  extensive 
skylight.  In  the  lighting  of  sculpture  it  should  be  noted  that 
the  position  of  the  light-source  determines  the  direction  of  the 
shadows;  the  solid-angular  extent  of  the  light-source  at  a  given 
point  determines  the  character  of  the  shadow-edges;  and  the 


166  THE  LIGHTING  ART 

diffused  light  from  the  surroundings  determines  the  brightness 
of  the  shadows.  Individual  rooms  or  alcoves  in  which  the 
object  may  be  properly  oriented  with  respect  to  the  light-source 
and  in  which  the  lighting  may  be  somewhat  controlled  repre- 
sents the  ideal  in  the  display  of  sculpture.  However,  such  a 
condition  is  rarely  practicable  so  that  the  objects  may  be 
placed  judiciously  in  a  sculpture  gallery  or  in  various  advantage- 
ous positions  in  the  museum.  In  general,  as  few  lighting-units 
as  possible  should  be  used  in  a  sculpture  gallery  and  the  sky- 
light-area should  be  made  of  such  an  area  that  its  solid-angular 
extent  is  not  too  great  to  cause  flattening  of  the  objects  or  too 
small  to  admit  sufficient  light.  If  a  sub-skylight  is  used  it 
should  be  satisfactory  to  flood  this  with  light  for  the  artificial 
illumination  of  crowded  sculpture  exhibits.  The  foregoing 
principles  are  the  chief  ones  but  most  details  must  be  worked 
out  for  each  specific  case. 

In  the  display  of  various  other  objects  the  same  general  prob- 
lems are  met.  In  rooms  containing  many  glass  cases  the  simple 
optical  law  of  reflection  should  be  considered  in  aiming  to  avoid 
annoying  reflected  images.  Vertical  glass  sides  through  which 
objects  may  be  viewed  generally  are  free  from  this  annoyance 
if  the  artificial  lighting  units  are  hung  high.  It  is  possible  to 
view  the  objects  through  three  vertical  glass  sides  of  a  case  if 
windows  are  confined  to  one  side  of  the  room. 

Many  valuable  objects  of  delicate  colors  are  found  to  fade 
under  daylight  illumination  and  insurance  against  this  may  be 
obtained  to  some  extent  by  using  certain  artificial-daylight 
units  owing  to  the  lower  amount  of  ultra-violet  energy  per 
lumen  as  compared  with  that  of  daylight.  Owing  to  the  many 
difficulties  encountered  in  the  control  of  daylight,  to  the  cost 
of  construction  of  extensive  skylights,  to  the  maintenance,  and 
to  the  fuel  consumption  directly  attributable  to  large  areas  of 
glass,  it  would  not  be  surprising  to  find  natural  daylight  gradu- 
ally giving  way  to  artificial  daylight  in  the  illumination  of 
art  treasures  and  other  valuable  objects. 

These  are  only  a  few  of  the  chief  points  pertaining  to  the 
lighting  of  museums  but  there  are  many  interesting  details. 
This  is  a  field  worthy  of  the  interest  of  the  lighting  specialist 


LIGHTING  IN  PUBLIC  BUILDINGS  167 

because  it  supplies  many-sided  problems  which  draw  upon  his 
scientific  and  artistic  ability. 

Auditoriums. — The  problem  of  lighting  in  such  interiors 
must  be  viewed  from  the  standpoint  of  the  audience  primarily 
although  there  should  be  some  consideration  for  those  on  the 
platform.  If  the  interior  is  particularly  decorative  the  lighting 
effects  should  be  in  harmony  with  the  architectural  and  decora- 
tive scheme  and  the  fixtures,  if  there  are  any  visible,  should 
also  be  in  harmony  with  the  whole.  Various  general  types  of 
lighting  are  applicable  to  auditoriums  depending  upon  the  con- 
ditions. It  is  perhaps  true  that  in  general  indirect  lighting 
from  concealed  sources  is  the  most  successful  from  the  stand- 
point of  eye  comfort  and  many  beautiful  effects  have  been 
obtained  by  this  system.  If  direct  or  so-called  semi-indirect 
units  are  used  they  should  be  hung  high  and  the  primary  light- 
sources  should  be  effectively  screened  from  view.  Glare  and 
discomfort  is  experienced  from  units  of  high  brightness  in 
comparison  with  their  backgrounds  even  though  an  image  of 
them  is  not  focused  upon  the  retina.  In  other  words,-  the  upper 
eyelid  may  screen  the  source  from  the  retina  but  the  glare  due 
to  a  high  intensity  of  illumination  on  the  eyelid  is  quite 
annoying. 

The  intensity  of  illumination  in  the  auditorium  should  be 
controlled  by  means  of  switches  and  in  many  cases  rheostatic 
control  is  desirable  in  order  to  change  the  intensity  gradually. 
Many  beautiful  effects  of  color  can  be  utilized  in  some  cases 
quite  appropriately.  Emergency  lighting  and  exit-lamps 
should  be  connected  preferably  to  an  auxiliary  service  which  is 
independent  of  the  main  supply  in  order  to  insure  the  safety  of 
the  audience  at  all  times.  Special  lighting  should  be  provided 
for  the  platform  in  order  that  the  speaker  may  be  more  intensely 
illuminated  than  the  audience.  If  enclosing  units  such  as 
lanterns  are  used  it  is  practicable  to  have  the  side  and  rear 
panels  of  denser  diffusing  glass  than  the  front  panels  and  vari- 
ous other  units  may  be  devised  to  give  an  asymmetrical  dis- 
tribution of  light. 

In  auditoriums,  windows  are  best  placed  on  the  two  sides  of 
the  audience  in  order  to  free  the  speaker  and  the  audience  from 


12 


168  THE  LIGHTING  ART 

the  ordeal  of  facing  windows.  Ceiling  skylights  may  be  used 
successfully  and  shades  should  be  available  for  controlling  the 
daylight. 

Churches. — All  of  the  problems  of  auditorium  lighting  are 
found  in  churches  with  many  additional  ones.  In  attacking  a 
problem  of  lighting  a  church  in  which  the  architectural  scheme 
is  such  an  important  aspect  it  is  well  to  be  familiar  with  the 
historical  development  of  the  particular  type  of  architecture  and 
with  the  characteristics  of  the  particular  creed  so  that  the 
lighting  effect  may  be  appropriate  for  the  spirit  of  the  interior. 
The  lighting  should  be  dignified,  impressive  and  congruous  and 
the  fixtures,  besides  being  of  proper  utilitarian  value,  should  be 
in  harmony  with  the  period  or  style  of  architecture.  No  field 
of  lighting  exemplifies  the  expressiveness  of  lighting  effects 
more  than  that  of  church-lighting.  Few  churches  should  ordi- 
narily be  illuminated  to  a  high  intensity  for  dim  light  is  con- 
ducive to  meditation  and  prayer  and  a  concentration  of  light 
on  the  chancel  tends  to  focus  the  attention  there.  The  lighting 
should  be  ecclesiastical  and  should  inspire  reverence  by  its 
solemnity.  Some  churches  have  ceilings  of  low  reflection-fac- 
tor and  this  loftiness  of  the  ceiling  should  not  be  destroyed  by 
light.  On  the  other  hand,  in  some  of  our  modern  churches  the 
ceiling  and  walls  are  of  high  reflection-factor  and  light  diffused 
over  all  the  areas  appears  to  be  symbolic  of  the  cheerfulness 
which  appears  to  be  a  dominant  note  in  the  creed.  In  this 
field  the  charm  and  expressiveness  of  tinted  light  may  be  effec- 
tively utilized  but  the  color  should  be  so  faint  as  to  be  felt  rather 
than  seen. 

In  the  case  of  natural  lighting  the  windows  should  be  pref- 
erably on  the  two  sides  of  the  audience.  Windows  in  the 
chancel  should  be  as  high  as  possible  and  of  deeply  stained  glass. 

The  artificial  lighting  of  churches  may  be  of  any  of  the  appro- 
priate types  if  proper  care  is  taken  to  avoid  high  brightnesses 
and  brightness-contrasts.  In  the  case  of  high  ceilings,  chan- 
deliers and  other  direct  lighting  units  may  be  satisfactory  but 
with  extremely  low  ceilings  indirect  units  or  other  means  of 
concealing  the  light-sources  should  be  adopted  if  possible. 
The  church  is  ordinarily  a  beautiful  interior  and  the  lighting 


LIGHTING  IN  PUBLIC  BUILDINGS  169 

units  should  be  placed  so  as  not  to  obscure  any  of  the  important 
details.  If  there  is  a  gallery  the  units  should  be  hung  suffi- 
ciently high  so  as  not  to  be  annoying  to  the  occupants.  Perhaps 
no  other  phase  of  lighting  calls  for  as  many  special  designs  of 
fixtures,  relatively,  as  church-lighting  in  order  to  meet  the  many 
different  conditions. 

The  altar  is  difficult  of  treatment  but  its  architectural  con- 
struction sometimes  permits  the  speaker  to  be  illuminated  by 
units  concealed  behind  a  cove  on  the  sides.  In  some  churches 
electric  candles  are  in  extensive  use  when  the  ritual  permits  their 
use.  The  intensity  of  illumination  in  the  chancel  should  be 
about  twice  that  in  the  auditorium  proper.  Dimmers  may  be 
employed  effectively  for  the  auditorium  lighting  and  at  least 
two  intensities  of  illumination  should  be  available  by  means  of 
switches. 

Many  other  details  of  lighting  are  found  in  churches  such  as 
the  illumination  of  the  organ-keyboard,  the  choir,  bulletin- 
boards,  clocks  and  even  electric  signs.  The  beauty  of  the  color 
of  stained  glass  windows,  only  visible  to  the  audience  by  light 
transmitted  inward,  may  be  enjoyed  at  night  by  flood-lighting 
them.  A  number  of  windows  have  been  flood-lighted  by  means 
of  artificial-daylight  lamps  and  the  contrast  with  the  yellowish 
interior  light  is  quite  pleasing. 

Theatres. — Many  of  the  problems  encountered  in  auditoriums 
and  churches  are  found  in  theatres  but  in  the  latter  case  a  touch 
of  the  spectacular  and  many  novel  effects  are  appropriate. 
Stronger  color-effects  are  permissible  than  in  other  auditoriums 
and  more  spectacular  dimming  arrangements  may  be  employed. 
A  common  annoyance  is  that  of  the  bright  orchestra -lamps  or 
even  the  highly  illuminated  music-racks  when  the  auditorium 
is  dark.  If  chandeliers  are  used,  tinted  lamps  appropriate  to 
the  decorative  scheme  may  be  employed  and  the  psychological 
effect  of  colored  light  may  be  utilized.  For  example,  during 
the  hot  summer  months  a  cold  blue-green  tint  is  quite  effective 
in  suggesting  coolness.  Emergency  and  exit-lights  are  usually 
demanded  by  law. 

The  moving-picture  theatre  presents  some  additional  prob- 
lems owing  to  the  continued  darkness  of  the  auditorium  and  to 


170  THE  LIGHTING  ART 

the  problems  of  projection.  In  entering  from  the  street  it  is 
advantageous  to  the  comfort  of  the  patron  to  have  the  intensity 
of  illumination  decrease  in  steps  to  the  darkness  of  the  audi- 
torium. Care  should  be  taken  to  have  the  orchestra-lamps  and 
music-racks  screened  from  the  audience  and  if  the  projection 
lantern  is  sufficiently  powerful  a  low  illumination  in  the  audi- 
torium is  desirable  from  standpoints  of  safety  and  of  eye- 
comfort.  The  picture-screen  is  often  too  bright  in  contrast 
with  that  of  the  surroundings  for  comfortable  viewing.  The 
flicker  on  the  screen  varies  approximately  with  the  logarithm 
of  the  brightness  of  the  screen  so  that  it  appears  well  to  reduce 
the  screen-brightness  as  far  as  compatible  with  satisfactory 
pictures.  Of  course  the  perfection  of  the  projection  apparatus 
is  a  factor  in  the  production  of  annoying  flicker.  The  reflecting 
characteristic  of  the  surface  of  the  screen  should  be  appro- 
priately chosen  according  to  the  dimensions  of  the  theatre. 
For  narrow  rooms,  the  screen  may  be  of  an  aluminized  finish  or 
of  any  finish  which  spreads  the  light  less  than  a  screen  painted 
with  flat  white.  A  screen  approaching  a  perfectly  diffusing 
surface  is  best  for  a  wide  theatre.  In  consideration  of  the 
comfort  of  the  audience  the  auditorium  lighting  should  be 
controlled  by  means  of  dimmers  so  that  the  intensity  may  be 
gradually  decreased  or  increased  respectively  before  and  after 
the  picture  is  presented.  The  screen  may  be  illuminated  with 
low  intensities  of  colored  light  with  excellent  results  if  these 
tints  are  properly  related  to  the  picture.  Usually  fairly  satu- 
rated colors  are  best  because  they  are  extremely  diluted  by 
mixture  with  the  projected  light.  The  environment  of  the 
screen  provides  opportunities  for  beautiful  lighting  effects. 


CHAPTER  XIX 
INDUSTRIAL  LIGHTING 

When  industrial  lighting  is  considered  from  the  broad  aspect 
of  vision,  the  lighting  specialist  is  confronted  with  many  diverse 
problems.  In  various  other  classes  of  interior  lighting  the 
problems  are  not  merely  confined  to  the  realization  of  a  given 
intensity  of  illumination  upon  a  certain  plane  but  involve  the 
esthetic  and  psychological  aspects.  In  industrial  lighting  the 
function  of  the  lighting  expert  is  not  merely  to  provide  a  given 
intensity  upon  a  certain  horizontal  plane  but  to  illuminate  the 
work  properly  without  glare,  to  insure  the  safety  of  the  work- 
man by  means  of  proper  lighting  and  to  protect  his  eyesight  by 
means  of  various  protective  glasses  and  other  devices.  Thus  it 
is  seen  that  the  problems  of  industrial  lighting  are  largely 
scientific  and  engineering. 

The  intensity  of  illumination  depends  upon  the  nature  of  the 
work  or  activity  and  inasmuch  as  no  other  method  of  determin- 
ing the  proper  intensity  is  available,  the  intensities  are  es- 
tablished by  actual  practice.  Apparently  there  is  no  reason 
why  much  higher  intensities  of  artificial  light  than  are  com- 
monly used  should  not  be  satisfactory  from  the  standpoint 
of  vision  and,  although  no  positive  proof  is  available,  there  is  a 
possibility  that  much  of  the  complaint  against  artificial  lighting 
may  be  due  to  insufficient  intensities  or  quantities  of  light.  It 
should  be  remembered  that  under  average  daylight  conditions 
the  illumination  intensities  are  much  greater  than  commonly 
encountered  under  artificial  lighting  and  that  the  eye  functions 
quite  differently  at  low  intensities  than  at  high  intensities. 
Although  the  changes  in  these  functions  begin  to  be  quite  notice- 
able in  general  at  brightnesses  corresponding  to  that  of  a  white 
surface  under  an  illumination  of  a  tenth  of  a  foot-candle  or  less, 
this  brightness  corresponds  to  that  of  surfaces  of  low  reflection- 
factors  under  an  illumination  of  a  foot-candle  or  more.  In 

171 


172  THE  LIGHTING  ART 

other  words,  the  visual  functions  are  dependent  upqn  brightness 
and  it  is  possible  under  ordinary  factory  conditions  of  lighting 
and  surroundings  that  ofttimes  the  eyes  are  expected  to  work  on 
"high"  when  they  are  really  in  "low."  This  is  an  aspect  of 
vision  which  has  not  been  given  much  attention  in  respect  to 
lighting  and  in  the  absence  of  more  definite  data  it  is  a  safe 
procedure  to  increase  the  intensities  of  illumination  provided 
the  light-sources  are  properly  shaded  and  other  precautions 
are  taken. 

The  engineering  aspects  of  industrial  lighting  have  been  sub- 
jected to  much  study  during  recent  years  and  the  lighting  special- 
ist is  usually  equipped  with  data,  experience,  and  precedents 
which  insure  an  excellent  design  wherever  he  has  the  oppor- 
tunity to  apply  his  knowledge.  A  few  of  the  aspects  which 
have  been  studied  will  be  noted  briefly. 

Proper  lighting  has  been  shown  to  increase  production.  In 
a  canvass  made  among  a  large  number  of  industrial  plants  in 
which  the  lighting  had  been  modernized,  a  considerable  per- 
centage reported  increased  production.  Many  reported  that 
their  operatives  were  better  satisfied  and  in  general  the  results 
were  such  as  to  increase  production  and  to  decrease  spoilage 
either  directly  or  indirectly. 

It  has  been  shown  that  inadequate  illumination  is  directly 
responsible  for  many  industrial  accidents  and  that  proper 
artificial  lighting  is  a  preventative  measure.  Statistics  reveal 
the  fact  that  the  percentage  of  industrial  accidents  are  more 
numerous  during  the  winter  months  when  daylight  is  often 
inadequate.  Artificial  lighting  is  an  obvious  remedy.  Re- 
cently protective  lighting  has  become  recognized  as  a  desirable 
feature  of  industrial  lighting  and  as  a  consequence  various 
methods  of  exterior  lighting  have  been  devised  as  an  aid  to 
watchmen.  Flood-lighting  projectors  are  playing  an  im- 
portant part  in  such  systems. 

The  system  of  illumination  to  be  employed  in  a  factory  de- 
pends upon  the  particular  conditions  but  general  direct-lighting 
is  strongly  advocated.  Such  a  system  of  illumination  is  not 
essentially  more  expensive  to  install  and  to  operate  than  a  hap- 
hazard system  of  localized  lighting.  In  fact,  records  show  that 


INDUSTRIAL  LIGHTING  173 

adequate  general  lighting  is  sometimes  obtained  at  a  lower  cost 
than  unsatisfactory  lighting,  with  the  resultant  increased  pro- 
duction and  less  spoilage  as  good  measure.  Local  units  which 
may  be  shifted  by  the  workmen  to  suit  their  desires  are  likely 
to  be  badly  placed  so  that  glare  results ;  time  is  wasted  in  making 
these  changes;  and  the  lamps  and  accessories  are  likely  to  be- 
come soiled  by  handling  them  which  reduces  the  effectiveness 
of  the  light-flux  which  is  generated.  If  a  localized-lighting 
system  is  subjected  to  a  proper  maintenance  it  is  likely  that  in 
most  cases  this  would  be  found  to  be  a  greater  item  of  expense 
than  that  attending  a  proper  maintenance  of  a  general-lighting 
system. 

There  is  a  period  of  the  day  when  daylight  is  waning  and  is 
being  reinforced  by  artificial  light  which  is  generally  unsatis- 
factory. There  may  be  several  reasons  for  this  but  the  question 
has  not  been  answered  completely.  In  the  design  of  a  factory 
the  machinery  is  either  laid  out  and  the  building  is  erected  about 
it  or  vice  versa.  In  either  case  there  is  no  doubt  that  the 
natural  lighting  is  more  or  less  considered  in  connection  with 
the  designs  and  layouts.  Besides  this  the  workman  naturally 
adjusts  his  position  somewhat  to  daylighting  conditions  and  as 
a  consequence  when  artificial  light  is  added  there  is  a  conflict  of 
shadows  due  to  the  generally  different  directions  of  natural  and 
artificial  light.  This  disturbance  naturally  lasts  until  artificial 
lighting  has  conquered  the  daylighting  and  the  workman  has 
become  adapted  to  it.  In  so  far  as  it  is  practicable,  the  artificial 
lighting  should  simulate  daylight  in  distribution  and  hence  in 
shadow-effects. 

Even  though  this  may  be  done  there  is  usually  the  disturbing 
influence  of  the  different  colors  of  the  two  illuminants.  The 
physiological  or  psychological  effect  of  this  unsatisfactory  color- 
difference  is  unknown  but  that  it  is  annoying  is  the  testimony 
of  many  observers.  The  difficulty  is  eliminated  by  using 
artificial  daylight  and  such  a  procedure  has  been  adopted  in 
some  offices  and  in  industrial  plants  even  where  the  discrimina- 
tion of  colors  is  not  of  great  importance.  Incidentally  one  of 
the  most  modern  developments  in  industrial  lighting  has  been 
the  recent  adoption  of  the  use  of  artificial  daylight  in  many 


174  THE  LIGHTING  ART 

plants.  It  is  surprising  to  many  to  learn  how  extensive  is  the 
factor  of  color-discrimination  in  the  industries.  This  is  not 
only  involved  in  textile  mills,  color-factories,  lithographing 
plants,  etc.,  but  also  in  a  vast  number  of  other  industries  such 
as  brass  works,  ore  refineries,  wood-working  factories,  etc.,  as 
shown  in  Chapter  XI. 

Glare  is  the  most  generally  annoying  feature  of  lighting  and 
it  is  not  completely  overcome  even  when  the  light-sources  are 
properly  shaded.  Proper  diffusion  or  reduction  of  the  bright- 
ness of  the  apparent  light-source  is  necessary  in  order  to  avoid 
the  annoying  reflections  of  light-sources  of  high  brightness  from 
polished  metals  and  other  glossy  surfaces.  Practically  no 
modern  light-sources  can  be  viewed  with  comfort  at  close 
range  or  when  directly  in  the  normal  visual  field.  If  the  light- 
sources  are  hung  sufficiently  high  and,  if  too  bright,  they  are 
properly  shaded  and  equipped  with  diffusing  media,  this  source 
of  glare  is  eliminated.  However,  if  the  background  is  too  dark 
there  still  may  be  present  an  annoying  glare  due  to  contrast. 
Ideal  conditions  of  maximum  brightness  have  been  suggested 
in  Chapter  V  but  for  factory  lighting  these  may  be  imprac- 
ticably low.  The  solution  then  is  to  hang  the  units  high.  This 
may  be  impracticable  in  many  cases  owing  to  obstructions  such 
as  belting,  shafting,  beams,  etc.,  so  that  compromises  must  be 
made.  In  any  case  the  lowest  practicable  brightness  should  be 
obtained  by  diffusing  media  if  necessary  and  the  units  should  be 
equipped  with  proper  shades. 

Some  modern  factories  are  so  laid  out  and  are  so  compara- 
tively free  from  obstructions  that  the  outlets  for  a  general  light- 
ing system  may  be  symmetrically  and  regularly  spaced  accord- 
ing to  aisles,  tables,  machines,  or  bays  and  the  lighting  problems 
are  practically  solved  on  selecting  the  reflectors  or  lighting  units 
which  give  the  proper  distribution  of  light  for  the  spacing  and 
hanging  height  and  on  computing  the  luminous  output  re- 
quired from  each  unit.  The  refinements  of  lighting  arise  in 
those  installations  in  which  various  machines  or  operations 
require  special  treatment.  For  example,  in  a  machine  shop 
where  machines  of  various  duties  cannot  be  arranged  in  uniform 
rows  or  from  the  nature  of  the  work  the  shadows  fall  from 


INDUSTRIAL  LIHGTING  175 

different  directions,  each  machine  should  be  lighted  more  or 
less  independently.  A  general  lighting  system  may  still  be 
used  but  the  outlets  must  be  spaced  according  to  the  locations 
of  the  machines.  This  treatment  might  be  called  "localized- 
general"  lighting.  If  the  units  are  hung  high  they  will  usually 
supply  adequate  lighting  on  the  less  important  parts  of  ma- 
chines, upon  aisles,  etc.  In  such  a  case  the  study  of  direction 
of  light  and  of  the  shadows  is  important. 

In  some  special  cases  an  additional  local  illumination  may  be 
required  but  when  this  is  resorted  to,  the  installation  should 
be  permanent  and  unalterable  by  the  operators.  The  light- 
sources  should  be  well  shaded  and  the  light  should  be  properly 
directed  to  the  important  point.  Examples  where  such  local 
units  are  being  used  satisfactorily  are  on  sewing  machines, 
work-benches  where  fine  work  is  done,  at  indicators  on  ma- 
chines, etc. 

The  control  of  various  circuits  or  of  individual  lighting  units 
by  means  of  switches  is  an  important  economic  factor  in  indus- 
trial lighting.  In  the  ideal  method  of  control  the  circuits  are 
as  numerous  as  necessary  in  order  to  provide  for  the  operation 
of  only  those  lighting  units  which  may  be  necessary  at  any 
particular  time.  Various  schemes  of  control  are  in  use  depend- 
ing upon  the  local  conditions;  however,  a  general  principle  is  to 
control  the  units  parallel  to  the  windows.  In  such  cases  the 
units  farthest  from  the  windows  may  be  lighted  first  because 
daylight  fails  at  such  points  before  it  does  nearer  the  windows. 
Adequate  control  is  a  desirable  feature  in  all  lighting  systems. 

The  maintenance  of  lighting  systems  is  perhaps  the  most 
neglected  feature  of  lighting.  After  a  satisfactory  system  has 
been  installed  it  is  economical  to  organize  a  definite  procedure 
in  inspecting,  in  cleaning  the  various  reflecting  and  transmitting 
portions  of  the  units,  and  in  replacing  burned-out  lamps  or 
broken  mantles.  It  is  even  economical  to  replace  lamps  and 
mantles  which  are  still  in  operation  but  which  have  so  deterio- 
rated as  to  have  passed  beyond  the  point  of  economical  opera- 
tion. The  depreciation  of  lighting  units  as  to  output  is  an 
unavoidable  feature  of  any  lighting  scheme  and  especially  is 
this  a  vital  factor  in  industrial  lighting.  The  surfaces  of  light- 


176  THE  LIGHTING  ART 

ing  units  which  are  depended  upon  to  reflect  and  to  transmit 
light  should  be  as  smooth  as  possible  if  they  are  exposed  to  the 
atmosphere  which  is  laden  with  dust  and  vapor.  Windows  and 
other  glass  skylights  are  commonly  washed  to  let  the  daylight 
in  but  this  custom  has  not  been  so  generally  in  vogue  with 
artificial  lighting  units.  It  has  been  shown  by  many  who 
have  kept  records  that  depreciation  in  the  efficiency  of  a  light- 
ing unit  is  an  ever-present  and  important  factor  in  industrial 
lighting  and  that  a  systematic  maintenance  is  a  profitable 
remedy. 

In  order  to  obtain  efficient  and  satisfactory  lighting,  the 
surroundings,  especially  the  ceiling,  should  be  finished  in  white 
or  in  a  light  tint  in  so  far  as  is  practicable.  This  increases  the 
utilization  efficiency  of  the  installation  and  often  reduces  or 
eliminates  glare  by  providing  a  background  of  a  sufficient 
brightness  to  reduce  the  brightness-contrasts  between  the 
lighting  units  and  the  background.  Such  surfaces  also  pro- 
vide a  more  cheerful  interior  and  the  specifications  of  their 
reflection-factors  and  colors  are  included  in  the  province  of  the 
activities  of  the  lighting  specialist.  Pleasing  and  restful  sur- 
roundings, which  also  have  a  degree  of  artistic  value,  are  ob- 
tained by  using  shades  and  tints  of  green.  The  ceiling  may  be 
white  or  a  very  light  tint  of  green  or  yellow.  The  upper  walls 
may  be  a  light  shade  of  an  unsaturated  green  and  the  lower  walls 
and  supporting  columns  may  be  of  a  moderate  shade  of  green 
or  olive.  The  same  scheme  may  be  used  in  respect  to  yellow 
with  pleasing  results.  The  upkeep  of  these  surroundings  is 
a  matter  of  maintenance  which  should  not  be  neglected. 

As  has  already  been  stated  the  lighting  problem  has  not  been 
solved  when  a  certain  intensity  of  illumination  has  been  pro- 
vided at  the  work-points  or  work-planes.  Proper  lighting 
finally  includes  proper  seeing  and  therefore  all  classes  of  work 
should  be  studied  in  detail.  For  example,  we  distinguish 
objects  by  discriminating  differences  in  light,  shade,  and  color. 
After  a  proper  quality  of  light  has  been  selected  it  should  be 
distributed  so  that  the  objects  are  properly  modelled  by  light 
and  shade.  Highly  directed  light  may  be  necessary  in  some 
cases  in  order  to  distinguish  small  metallic  objects  by  their  high- 


/     INDUSTRIAL  LIGHTING  177 

lights  or  to  examine  the  polish  of  surfaces.  In  other  cases 
highly  diffused  light  from  apparent  sources  of  low  brightness  is 
best  from  the  standpoint  of  the  lack  of  shadows  and  of  glare 
due  to  reflected  images. 

Furthermore,  the  background  is  an  important  factor  in 
providing  contrasts  in  brightness  for  viewing  small  objects. 
Often  operators  are  seen  doing  fine  work  which  makes  the 
severest  demand  upon  the  ability  of  the  eye  to  discriminate 
fine  detail,  under  conditions  which  subject  their  eyes  to  strain 
owing  to  an  accidental  background  consisting  of  an  array  of 
miscellaneous  objects.  For  fine  work  a  background  should  be 
provided  which  is  of  uniform  brightness  and  of  a  suitable  color. 
If  the  fine  details  are  best  seen  as  dark  objects  against  a  light 
background  the  latter  should  be  provided.  If  they  are  seen 
more  easily  as  bright  objects,  a  dark  background  should  be 
specified.  It  should  be  noted  that  the  brightness  of  a  back- 
ground is  co-dependent  upon  its  reflection-factor  and  upon  the 
intensity  of  illumination.  The  degree  of  contrast  may  be  best 
determined  by  experiment  although  judgment  is  a  valuable 
asset.  Experiments  on  the  color  and  brightness  of  backgrounds 
have  been  performed  but  owing  to  the  variety  of  conditions 
encountered  no  general  specifications  can  be  offered.  In  the 
case  of  a  certain  operation  gray,  green,  or  buff  backgrounds  were 
found  to  be  desired  depending  somewhat  upon  the  operator. 
Severe  headaches  due  to  eyes  train  were  entirely  eliminated  in 
this  case  by  supplying  uniform  backgrounds  against  which  the 
work  was  viewed.  This  point  is  of  considerable  importance 
in  the  industries  but  the  consideration  of  background  has  been 
much  neglected. 

In  many  industrial  processes  the  eyes  are  subjected  to  the 
dangers  of  flying  particles,  to  excessive  heat,  to  high  bright- 
nesses, or  to  excessive  and  harmful  ultra-violet  rays.  Safety 
glasses  should  be  specified  for  safeguarding  the  eyes  under 
such  conditions.  Protection  from  flying  particles  may  be 
secured  by  using  thick  clear  lenses  mounted  in  approved  holders. 
Clear  glass  lenses  serve  materially  to  protect  the  eyes  from  ex- 
cessive heat  which  might  burn  the  delicate  membranes  of  the 
eye.  It  has  not  been  proved  that  infra-red  rays  are  harmful 


178  THE  LIGHTING  ART 

to  vision  but  it  is  a  safety  measure  in  certain  processes  to 
specify  the  use  of  glasses  which  are  of  low  transmission-factor 
for  these  rays .  Ordinary  ' '  smoke ' '  glasses  of  various  ' '  shades ' ' 
or  transmission-factors  are  available  for  reducing  the  bright- 
ness of  the  retinal  image  to  a  safe  value.  The  author  has 
worked  out  a  series  of  combinations  of  different  shades  of 
"smoke"  glass  with  a  glass  which  absorbs  harmful  ultra-violet 
rays  for  various  industrial  processes  on  the  basis  of  the  bright- 
nesses and  intensities  of  ultra-violet  energy  involved.  If  there 
were  a  rigid  standard  of  shades  of  smoke  glass  such  a  series 
would  be  of  extreme  value  to  the  industrial  manager,  to  the 
lighting  specialist  and  to  others.  This  question  cannot  be 
discussed  in  detail  here  but  there  are  several  discussions  of 
value  to  be  found  elsewhere.1  The  chief  precaution  is  not  to 
judge  the  protective  value  of  a  glass  for  invisible  energy  such  as 
ultra-violet  and  infra-red  rays  by  a  mere  visual  inspection. 

The  intensities  of  illumination  to  be  specified  in  the  industries 
depends  upon  the  character  of  the  work  and  can  be  determined 
only  from  experience.  For  reasons  already  discussed  it  ap- 
pears to  be  a  safety  measure  to  increase  the  intensities  of 
illumination  as  far  as  is  compatible  with  economy,  to  shade 
bare  light-sources  from  the  eyes,  and  to  apply  diffusing  media 
in  order  to  reduce  the  brightness  and  brightness-contrasts. 
The  practice  in  industrial  lighting  at  present  is  discussed  further 
in  Chapter  XXII. 

Reasonable  uniformity  of  illumination  over  general  work- 
planes  is  desirable  from  the  standpoint  of  eye-comfort,  safety 
and  production.  In  this  respect  daylight  is  generally  inferior 
to  the  best  possibilities  of  artificial  lighting  except  in  those  fac- 
tories where  adequate  skylight-area  is  available.  But  this 
deficiency  of  daylighting  is  somewhat  compensated  in  many 
places  by  the  quantity  of  light-flux  available  and  by  its  diffusion. 
Refractive  and  diffusing  glasses  may  be  used  to  advantage  in 
directing  or  scattering  natural  light  into  the  remote  places  and 


^M.  LUCKIESH:  Trans.  I.  E.  S.,  9,  472,  1914:  Electrical  World,  62,  844,  1913, 
and  66,576, 1915.  VERHOEFF  and  BELL tProc.Amer.Acad.  of  Arts  and  Sciences, 
51,  629,  1916.  COBLENTZ  and  EMERSON,  Tech.  Paper  93,  Bull.  Bur.  Stds.,  1917. 


INDUSTRIAL  LIGHTING  179 

in  eliminating  the  glare  from  the  sun  and  the  sky  and  the 
localized  high  intensities  of  direct  sunlight. 

In  the  foregoing  it  has  been  the  aim  to  present  the  chief 
principles  and  advantages  of  proper  lighting.  As  in  other 
chapters,  the  space  has  been  devoted  to  a  discussion  of  these 
principles  which  will  always  be  the  guides  of  the  lighting 
specialist  instead  of  giving  space  to  engineering  data  and  de- 
scriptions of  specific  cases  whose  value  is  only  temporary. 
Everyone  engaged  or  interested  in  lighting  may  obtain  the 
current  data  on  illuminants,  illuminating  devices,  and  layouts, 
from  the  bulletins  and  catalogues  of  manufacturers  which  are 
issued  as  new  lighting  equipment  appears  on  the  market. 
Throughout  this  book  it  has  been  the  aim  to  stimulate  the  con- 
sideration of  the  broader  view  of  lighting  and  to  record  ideas 
and  suggestions  which  may  aid  in  building  the  foundation  of 
creative  work  in  a  field  of  wonderful  opportunities. 


CHAPTER  XX 
STAGE-LIGHTING 

It  is  difficult  for  one  who  has  studied  the  possibilities  of  light, 
shade,  and  color  as  a  means  of  expression  and  as  an  accom- 
paniment to  the  play,  to  suppress  a  critical  attitude  toward  the 
crudity  of  lighting  effects  on  the  present  stage,  the  lack  of 
scientific  knowledge  in  utilizing  the  latent  possibilities  of  light- 
ing, the  crude  realism  demanded  by  the  public  and  therefore 
by  producers,  and  the  lack  of  appreciation  of  the  functions  of 
the  lighting  and  setting  in  relation  to  the  play.  The  material 
desired  in  a  discussion  of  the  present  subject  is  doubtless  that 
which  may  aid  the  lighting  specialist  in  providing  the  lighting 
to  meet  the  demands  of  producers  in  general;  therefore  much 
of  the  discussion  will  be  confined  to  criticisms  and  to  descrip- 
tions of  present  stage-lighting.  However,  the  greater  artistic, 
expressive,  and  psychological  possibilities  of  lighting  will  be 
touched  upon  as  well  with  the  hope  of  adding  something  to  the 
efforts  of  the  gallant,  though  small  band  of  stage  artists,  who  are 
striving  to  realize  a  harmony  of  lighting,  setting,  and  drama  in 
the  so-called  modern  theatre.  Little  groups  are  found  here  and 
there  undergoing  sacrifices  for  a  cause  which  bears  fruit  if  it 
does  no  more  than  point  out  some  of  the  incongruities  in  the 
lighting  and  in  the  setting  of  the  present  stage.  The  fault  lies 
with  the  public,  for  producers  cater  to  the  public's  taste;  there- 
fore the  present  stage  will  not  be  remodelled  in  lighting  and  in 
setting,  faster  than  is  warranted  by  the  change  in  the  apprecia- 
tion of  the  public. 

To  those  who  have  not  glimpsed  the  methods  employed 
"behind  the  scenes"  in  obtaining  lighting  effects  it  perhaps 
appears  strange  to  learn  that  the  present  stage-lighting  is 
crude  and  the  results  are  more  or  less  accidental  when  they  recall 
some  of  the  wonderful  lighting-effects  which  they  have  witnessed. 
But  these  effects  are  obtained,  as  a  rule,  by  trial  instead  of  by 

180 


STAGE-LIGHTING  181 

i  • 

the  direct  course  which  results  from  an  acquaintance  with  the 
art  and  science  of  color.  Furthermore,  little  thought  is  ap- 
parently given  to  the  emotional  value  of  light,  shade,  and  color. 
Demonstrations  of  lighting  effects  before  the  public  convince 
one  that  any  effect,  well-manipulated  and  striking,  appeals 
to  the  general  public  regardless  of  its  deeper  relation  to  the  scene 
or  action.  For  this  reason  lighting  has  great  possibilities  in 
commanding  the  attention  of  the  public. 

The  lighting  of  a  stage-setting  may  be  divided  into  distribu- 
tion and  quality  of  light,  and  in  order  directly  to  produce  the 
effect  which  is  born  in  the  imagination,  a  knowledge  of  the 
principles  of  control  of  light  and  of  the  mixture  of  colors  (both 
of  pigments  and  of  illuminants)  are  necessary.  These  have 
been  discussed  briefly  in  this  book  and  have  been  described  in 
detail  elsewhere.  Numberless  effects  of  distribution  of  light 
lie  between  the  extremes  of  diffusion  and  directedness  or  con- 
centration.1 Actors  may  be  silhouetted  against  a  bright 
background  or  may  be  brightly  illuminated  against  a  dark 
ground.  Between  these  extremes  are  found  numberless  ex- 
pressions of  light.  The  possibilities  of  color  are  likewise  infinite 
in  variety  and  the  stage  should  be  provided  with  elaborate 
apparatus  for  controlling  these  two  aspects  of  lighting. 

The  chief  equipments  for  a  stage  are  rheostats,  foot-lights, 
border-lights,  side-lights,  flood-lights,  and  spot-lights.  Not- 
withstanding the  fact  that  tremendous  wattages  are  required  in 
obtaining  brilliant  color-effects,  light  is  ordinarily  used  very 
inefficiently  on  the  stage.  Proper  reflectors  are  extremely 
advantageous  in  such  places  as  the  borders  but  their  use  is 
relatively  rare.  Crude  troughs  and  even  less  efficient  accessories 
are  the  more  common,  although  well-designed  troughs  of  para- 
bolic cross-section  meet  some  requirements  very  satisfactorily. 
In  a  few  cases  the  principles  of  efficient  and  proper  lighting  have 
been  introduced  upon  the  stage  by  lighting  specialists,  an 
excellent  example  of  such  work  in  this  country  being  that  of 
Bassett  Jones2  who  has  developed  several  novel  and  efficient 
lighting  accessories. 

1  M.  LUCKIESH:  "Light  and  Shade,"  1916. 

2  Electrical  World,  66,  1915:  Trans.  I.  E.  S.,  II,  1916. 


182  THE  LIGHTING  ART 

It  is  unnecessary  to  discuss  the  equipment  which  is  available 
for  stage-lighting  effects  because  complete  descriptions  may  be 
obtained  from  catalogues.  However,  it  should  be  noted  that 
in  this  field  the  ingenious  lighting  specialist  will  find  applica- 
tions for  an  extensive  knowledge  of  details  of  the  control  of 
light  and  of  color.  In  amateur  or  temporary  productions, 
novel  expedients  are  especially  applicable  owing  to  the  usual 
unavailability  of  standard  equipment.  In  such  cases  even 
dimmers  are  not  always  essential  because  beautiful  effects  may 
be  obtained  by  moving  templates  or  louvers  before  an  extended 
light-source.  For  example,  suppose  it  is  necessary  to  simulate 
a  camp-fire.  Even  on  the  professional  stage  this  is  usually  done 
by  covering  an  incandescent  lamp  with  a  tinted  fabric  and 
piling  about  it  the  fire- wood.  Thus  the  "fire"  burns  with 
steady  unrealism,  whereas  a  simple  arrangement  of  a  diffusing 
glass  or  paper  over  which  a  template  is  moved  manually  pro- 
vides a  striking  and  artistic  effect.  Colored  lights  may  be  mixed 
effectively  in  this  manner  or  by  means  of  louvers. 

One  of  the  severest  criticisms  of  stage-lighting  from  an  artistic 
standpoint  may  be  directed  against  the  use  of  foot-lights  for 
obtaining  the  dominant  light.  A  dominant  light  directed 
upward  from  below  the  horizontal  produces  unnatural  and 
even  grotesque  modelling  of  the  actors'  features  and  is  incon- 
gruous with  other  real  and  painted  effects  of  light  and  shade. 
Owing  to  present  construction  it  is  quite  impossible  to  obtain 
a  dominant  light  from  above  for  the  proper  lighting  of  the  front 
of  the  stage  but  worthy  attempts  have  been  made  to  do  so 
by  constructing  a  hood  extending  outward  into  the  auditorium 
from  the  upper  part  of  the  proscenium  arch.  Other  attempts 
have  been  made  to  obtain  the  desired  directed  light  from  the 
" front  of  the  house'7  but  such  lighting  usually  leads  to  "flat" 
effects.  Nevertheless,  there  is  more  experimental  work  to  be 
done  and  it  seems  that  this  is  one  of  the  many  fields  where  the 
architect  and  the  lighting  specialist  may  cooperate  with  the 
possibility  of '  solving  a  difficult  problem.  However,  even 
though  a  method  may  be  devised  for  obtaining  dominant  light 
from  above  the  horizontal,  the  foot-lights  must  be  retained,  for 
they  would  be  invaluable  in  contributing  those  "fogs"  of  dif- 


STAGE-LIGHTING  183 

fused  light  in  conjunction  with  border-lights  and  side-lights, 
which  are  necessary  for  illuminating  the  shadows. 

Incidentally,  such  "fogs"  of  light,  if  colored  and  of  sufficient 
intensity,  provide  a  means  for  obtaining  extremely  striking  and 
appropriate  effects.  For  example,  if  an  object  or  stage-setting 
be  flooded  with  a  high  intensity  of  red  light  and  a  highly  directed 
white  light  be  superposed,  the  shadows  will  remain  a  deep  shade 
of  red  and  the  high-lights  will  apparently  be  white.  By  the  use 
of  various  colors  of  diffused  light  or  even  of  various  beams  of 
light  of  different  colors  directed  from  various  points,  striking 
effects  may  be  obtained.  For  example,  imagine  blue  and  yellow 
lights  directed  from  different  points  toward  the  rear  of  the  stage. 
Where  both  these  colored  illuminants  mix  in  the  proper  pro- 
portions a  synthetic  white  light  results.  Thus  the  high-lights 
on  the  folds  of  a  garment  would  be  illuminated  by  white  light 
and  the  shadows  would  receive  either  blue  or  yellow  light  or 
various  mixtures.  Such  effects  are  very  beautiful  and  if,  for 
example,  dancers  are  moving  about  the  mobility  of  the  color- 
effects  is  very  enlivening  to  the  picture.  These  effects  represent 
a  step  further  in  painting  with  light  and  no  field  offers  greater 
opportunities  for  such  applications  than  stage-lighting. 

A  number  of  types  of  equipment  are  available  for  foot-lights 
but  the  trough  reflector  is  a  basic  principle  of  nearly  all  of 
these.  However,  it  appears  that  a  more  elaborate  switching 
control  of  the  " white"  foot-lights  would  be  desirable  in  order 
to  obtain  a  degree  of  directedness  laterally,  or  at  least  an  asym- 
metry of  lighting  which  is  the  basis  of  many  artistic  effects. 
The  modern  high-efficiency  tungsten  lamps  should  be  used  more 
in  foot-lighting  equipment,  but  one  disadvantage  is  the  high 
temperature  of  the  bulbs  which  rapidly  deteriorates  the  super- 
ficial coloring  which  is  commonly  used.  Colored  glass  filters 
could  be  used  to  advantage  but  owing  to  the  wide  variety  in 
the  colored  lights  demanded  this  is  not  always  practicable 
owing  to  the  usual  limitations  of  the  two  or  three  circuits 
provided. 

Owing  to  the  apparent  advantages  of  a  permanent  foot-light 
equipment  it  appears  that  a  determined  effort  should  be  made 
to  provide  four  circuits,  namely,  for  clear  lamps,  and  for  red, 

13 


184  THE  LIGHTING  ART 

green  and  blue  illuminants.  By  using  modern  tungsten 
(Mazda  C)  lamps  the  required  intensities  of  illumination  could 
be  obtained  from  the  fewer  number  of  outlets  which  would  be 
available  owing  to  the  limitations  of  space.  By  mixing  these 
four  illuminants  by  means  of  dimmers  any  intensity  of  any  de- 
sired tint  could  be  obtained  and  the  installation  could  be 
permanent  by  using  colored  glass  niters  in  the  form  of  caps  or 
plates.  It  is  hoped  that  colored  bulbs  of  sufficiently  pure 
and  correct  colors  will  be  available  in  the  near  future  for  these 
will  greatly  reduce  the  difficulties  in  securing  permanent  equip- 
ment and  in  realizing  the  best  effects  possible.  The  usual 
equipment  provides  white,  blue,  and  red  illuminants  but  the 
colored  lights  obtainable  from  these  are  much  less  limited  than 
from  the  preceding  four  illuminants.  If  only  three  circuits  are 
available  a  blue-green  and  an  orange-red  may  be  used  with  white 
if  the  aim  is  to  obtain  the  greatest  variety  in  color  from  three 
circuits. 

Quite  the  same  discussion  applies  to  permanent  border-lights 
and  side-lights.  Apparently  the  advantages  of  such  a  system 
have  not  been  generally  recognized  but  inasmuch  as  there  are 
no  insurmountable  obstacles  at  present  it  appears  that  there 
should  be  a  tendency  toward  the  adoption  of  such  a  system 
which  is  the  scientific  solution  of  stage-lighting  designed  to 
meet  a  vast  variety  of  requirements.  Of  course,  the  extensive 
use  of  yellow  or  amber  light  casts  some  doubt  upon  the  de- 
sirability of  obtaining  this  color  inefficiently  by  mixing  red  and 
green  lights  instead  of  obtaining  it  directly,  but  the  foregoing 
discussion  is  based  upon  the  premise  that  permanency  and 
flexibility  are  more  important  factors  in  stage-lighting  equip- 
ment than  efficiency  of  light-production. 

The  color-wheel,  which  consists  of  a  number  of  sectors  of 
colored  glass  or  gelatines,  and  various  movable  color-screens 
have  many  uses  in  stage-effects  and  may  be  used  advanta- 
geously in  other  fields.  Miniature  lamps,  swinging  or  blinking, 
have  their  applications.  Apparatus  is  available  for  simulating 
lightning  which  has  often  been  done  by  bringing  carbon  and 
iron  electrodes  into  contact.  Gauze  screens  play  many  parts 
on  the  stage  for  producing  various  illusions  but  their  use  in- 


STAGE-LIGHTING  185 

volves  lighting  almost  entirely.  Projection  apparatus  and 
slides  contribute  much  toward  the  success  of  some  of  the  most 
scenic  productions  and  even  the  rainbow  as  produced  by  a  glass 
prism  has  been  used.  The  many  lighting  effects  employed  on 
the  stage  are  too  numerous  to  embody  in  this  discussion  but 
they  are  always  produced  by  the  application  of  a  few  simple 
principles  of  the  control  of  the  distribution  and  color  of  light. 
In  many  ways  the  new  incandescent  lamps  are  likely  to  revolu- 
tionize stage-lighting  because  of  their  ease  of*  control,  of  their 
application  to  projection  apparatus,  and  of  their  high  luminous 
intensities.  Alternating-current  arcs  are  often  annoying  ow- 
ing to  their  " singing"  and  direct-current  arcs  require  constant 
attention.  If  reflecting  surfaces  are  used  the  mirror  is  most 
suitable  to  the  control  of  light,  but  such  diffusing  media  as  the 
aluminized  surface  are  best  for  diffused  lighting.  Many  simple 
expedients  may  be  resorted  to  in  order  to  prolong  the  life  of 
the  colored  gelatines  which  are  so  extensively  used  for  color- 
effects  in  stage-lighting.  These  in  general  involve  the  tjasic 
principle  of  having  most  of  the  undesired  radiant  energy  ab- 
sorbed by  other  media  which  are  uninfluenced  by  light  and 
to  provide  a  free  circulation  of  air  between  these  media  and  the 
colored  gelatines  as  shown  in  Fig.  8. 

For  outdoor  productions  the  so-called  flood-lighting  units  are 
extensively  used.  Often  it  is  desirable  to  eliminate  the  cone 
of  direct  light  in  order  to  confine  the  light  to  the  useful  beam 
and  to  prevent  the  annoyance  of  the  stray  light  which  is  not 
confined  to  the  beam.  This  is  effectively  done  by  using 
cylinders  of  blackened  metal  concentric  with  the  axis  of  the 
beam  or  unit.  Such  screens  may  be  fastened  very  easily  to 
any  projector  unit.  In  outdoor  productions  ordinary  reflectors, 
having  enamelled  or  aluminized  surfaces,  are  satisfactory  for 
foot-lights,  for  flood-lamps  of  short  range,  and  for  various  other 
uses  on  or  near  the  stage.  Metal  guides  may  be  fastened  to 
these  metal  reflectors  and  in  these  the  color-slides  may  be 
fixed  or  moved. 

Inasmuch  as  the  science  and  art  of  lighting  in  general  has  not 
invaded  the  stage  sufficiently  even  to  introduce  efficient  light- 
ing accessories  such  as  well-designed  reflectors  and  pure  color- 


186  THE  LIGHTING  ART 

ing  media,  it  requires  temerity  to  suggest  that  the  stage  artist 
familiarize  himself  with  the  science  of  color-mixture  and  with 
the  spectral  characteristics  of  the  colored  media  which  he  uses 
or  which  are  available.  Nevertheless,  he  will  ever  work  blindly 
until  he  gains  such  knowledge.  He  should  study  his  coloring 
materials  with  a  spectroscope  or  should  have  them  analyzed 
by  means  of  a  spectrophotometer.  The  data  yielded  by  such 
analyses  provide  a  working  knowledge  for  the  application  of 
these  materials.  In  a  similar  manner  he  should  realize  that 
the  color  of  an  object  is  influenced  by  the  spectral  character  of 
the  illuminant.  In  such  matters  the  eye  alone  is  not  capable 
of  supplying  the  analytical  data  required,  for  it  is  a  synthetic 
apparatus  in  respect  to  color.  He  should  be  familiar  with  the 
laws  of  color-mixture  which  are  quite  different  for  pigments  than 
for  illuminants.  In  the  case  of  pigments  the  resultant  color 
of  a  mixture  is'  due  to  subtraction  or  absorption  of  various 
spectral  components  and  the  resultant  color  is  that  which  is 
reflected  or  transmitted  in  common  by  the  colored  media  of  the 
mixture.  The  superposition  of  colored  glasses  or  gelatines  is 
governed  by  the  same  laws  of  color-mixture  as  the  mixing  of 
pigments.  Thus,  yellow  and  blue  glasses  superposed  result 
in  a  green  color  and  the  result  is  quite  the  same  with  pigments. 
The  primaries  of  this  method  of  color-mixture  are  purple,  yellow, 
and  blue-green. 

In  the  mixture  of  colored  illuminants  the  resultant  color  is 
that  due  to  an  addition  of  the 'components.  In  the  case  of 
adding  blue  and  yellow  illuminants  the  resultant  color  will  be 
white  if  the  proper  balance  is  obtained.  The  primaries  of  the 
additive  method  of  color-mixture  are  red,  green,  and  blue  and, 
by  varying  the  proportions  of  these  components  in  a  mixture, 
a  great  variety  of  hues  may  be  obtained  even  with  impure 
or  unsaturated  colored  illuminants  available  in  practice.  This 
aspect  of  the  science  of  stage-lighting  should  not  be  ignored  by 
the  stage  artist  who  hopes  to  avail  himself  of  the  dormant 
possibilities  of  lighting.  An  extensive  treatment  of  the  science 
and  art  of  color  would  be  out  of  place  here  but  such  will  be 
found  elsewhere. 

The  stage  artist  will  find  a  delightful  field  for  applying  a 


t  STAGE-LIGHTING  187 

knowledge  of  scientific  and  artistic  lighting  to  such  miniature 
stages  as  the  shadowgraph,  the  marionette  theatre,  and  various 
other  small  stages.  Some  of  these  present  problems  as  diffi- 
cult to  solve  as  those  encountered  on  the  normal  stage. 

There  are  many  incongruities  to  be  found  in  stage-effects  not 
only  in  respect  to  lighting  but  also  to  scenery  and  setting. 
Many  of  these  are  due  to  the  attempts  toward  realism.  For 
example,  the  painted  perspective  cannot  in  general  coincide 
with  the  real  perspective.  Gauze,  sky-domes,  and  various 
lighting  effects  amid  plain  surroundings  go  farther  toward  the 
realization  of  distance  and  atmosphere  than  attempts  in  realism 
by  means  of  painted  perspective.  Likewise,  the  painted 
shadows,  in  general,  are  not  in  harmony  with  the  real  shadows. 
It  is  safer  in  seeking  for  harmony  of  play,  of  setting,  and  of 
lighting  to  abandon  the  crude  realism  for  the  simplest  surround- 
ings and  the  art  of  the  stage  will  be  advanced  by  applying 
thought  and  research  to  new  expedients  and  to  the  expressive 
possibilities  of  lighting.  The  latter  are  found  in  light,  shade, 
and  color  effects  directed  artistically  and  scientifically  with  the 
psychological  aspect  of  the  action  and  mood  of  the  play  fore- 
most in  the  mind  of  the  stage  artist.  The  stage  is  a  most  ex- 
cellent place  to  paint  with  light. 

One  of  the  superior  features  of  light  as  an  expressive  medium 
is  the  ease  with  which  mobile  effects  may  be  obtained.  A 
painting  on  canvas  is  fixed  and  it  can  never  be  more  than  a 
representation  of  a  momentary  thought  or  scene.  The  artist 
may  suggest  motion  or  action  but  the  imagination  of  the  ob- 
server must  supply  the  remainder.  Technically  a  painting  is 
a  cross-sectional  view  of  the  flow  of  thought  or  action;  however, 
the  mobility  of  lighting  effects  greatly  extend  the  expressiveness 
of  a  scene.  The  fixed  painting  is  analogous  to  a  chord  in  music 
and  the  successions  of  effects  due  to  mobile  lighting  comprise  a 
symphony  of  lighting.  In  this  direction  the  stage  artist  may 
explore  a  vast  unknown  from  which  we  may  confidently  expect 
some  novel,  artistic,  and  psychological  developments.  Mobile 
lighting  is  not  new  in  our  experience  for  the  thoughtful  observer 
will  find  it  everywhere  in  Nature.  In  a  sense  we  experience 
some  of  the  pleasure  of  mobile  color  as  our  eyes  rove  over  a  rug 
or  painting  or  other  colored  object.  However,  the  language 


188  THE  LIGHTING  ART 

of  color  is  not  well  enough  known  to  justify  some  of  the  brazen 
attempts  which  have  been  made  in  mobile  color.  It  is  dis- 
couraging to  note  these  feeble  and  superficial  attempts  which 
have  been  made  to  relate  mobile  color  and  music  on  the  basis  of 
similarities  in  technique  and  in  other  respects.  However, 
color  is  appealing  to  mankind  and  is  influential  in  various  ways 
on  the  human  organism  so  that  mobile  color  may  take  its 
proper  place  in  company  with  music,  dancing,  painting,  and 
other  modes  of  appeal.  This  aspect  is  discussed  further  in 
Chapter  XXIV. 

The  stage  as  a  whole  is  a  mobile  picture  and  for  this  picture  all 
the  ingenuity  of  the  stage  artist  should  be  drawn  upon.  The 
whole  is  an  illusion  or  at  least  it  is  the  aim  that  it  should  be. 
The  preceding  discussion  has  been  confined  chiefly  to  lighting 
but  scenery  and  furnishings  are  closely  allied  to  lighting.  The 
scenery  should  be  painted  and  the  actors  costumed  with  a  defi- 
nite idea  of  the  lighting  effects  in  mind  because  the  changes  in 
the  color  of  the  light  are  accompanied  by  changes  in  the  colors 
of  the  dyes  or  pigments  in  the  setting.  Sometimes  these  latter 
changes  are  unsatisfactory.  It  is  beyond  the  scope  of  this 
book  to  dwell  upon  the  many  details  of  color-science  which  may 
be  applied  here  such  as  dyes  having  the  property  of  fluorescence 
or  other  characteristics  but  there  are  many  such  applications 
to  the  infinite  variety  of  problems  which  arise  on  the  stage. 
However,  in  closing  it  may  be  of  interest  to  mention  the  possi- 
bilities of  obtaining  disappearing  effects  and  complete  changes 
in  scenery  as  originated  by  the  author  a  number  of  years  ago. 
By  choosing  coloring  media  of  certain  desirable  physical  char- 
acteristics and  by  properly  employing  them  in  painting  certain 
parts  of  a  scene,  complete  changes  in  the  latter  may  be  accom- 
plished if  the  spectral  characters  of  the  illuminants  are  properly 
related  to  those  of  the  pigments.  In  other  words  two  scenes 
may  be  painted  on  the  same  canvas  and  one  will  disappear 
under  one  illuminant  and  the  other  will  be  brought  out  in  sharp 
contrast.  Under  the  other  illuminant  the  reverse  is  true. 
More  than  two  complete  changes  are  possible  but  great  diffi- 
culties arise  when  moire  than  two  are  attempted.  For  a  de- 
scription of  this  the  reader  should  refer  to  another  source.1 

1M.  LUCKIESH:  "Color  and  Its  Applications,"  1915,  p.  272. 


CHAPTER  XXI 
SPECTACULAR  LIGHTING 

There  are  many  opportunities  for  employing  light  for  the 
purpose  of  obtaining  spectacular  effects  and  many  other  effects 
which  may  not  be  classed  as  spectacular  but  whose  primary 
purpose  is  to  attract  attention.  These  problems  may  be  best 
viewed  from  the  standpoint  of  light,  shade,  and  color  as  is  the 
case  with  nearly  all  lighting  problems.  Accessories  of  many 
designs  are  available  for  obtaining  a  vast  variety  of  distribu- 
tions of  light  but  the  color  effects  are  difficult  to  obtain  at 
present  owing  to  the  inefficiency  in  the  production  of  colored 
light  and  to  the  scarcity  of  color-screens  which  are  permanent 
and  easily  adaptable.  There  is  a  need  for  such  color-screens 
and  colored  lamps  which,  as  it  grows  more  urgent,  will  doubtless 
be  met  by  manufacturers,  but  in  the  meantime  the  pioneer  in 
certain  fields  of  lighting  must  strive  under  the  handicap  of 
devising  various  accessories.  For  this  reason  the  development 
of  certain  aspects  of  lighting,  which  may  best  be  included  in 
this  chapter,  is  somewhat  deterred.  In  the  case  of  a  problem 
of  large  magnitude  such  as  the  lighting  of  the  Panama-Pacific 
Exposition  it  is  practicable  to  develop  the  various  accessories 
which  are  necessary  in  order  to  tap  the  resources  of  lighting 
possibilities,  but  the  lighting  specialist  does  not  always  feel 
justified  in  doing  this  in  the  cases  of  lesser  magnitude.  How- 
ever, many  opportunities  pass  by  daily  which  should  be  grasped 
by  those  interested  in  the  development  of  lighting-practice. 

Perhaps  the  most  extensive  field  of  lighting  which  may  be 
classed  as  spectacular  is  the  lighting  of  exteriors  of  buildings, 
monuments,  and  other  architectural  works.  It  is  often  a  pri- 
mary aim  in  such  lighting  to  attract  attention  but  many  cases 
may  be  justified  on  a  sounder  basis.  For  example,  many  per- 
sons seldom  have  an  opportunity  for  viewing  some  of  the  archi- 
tectural works  of  art  such  as  monuments  and  buildings  except 
at  night  and  the  expense  of  flood-lighting  them  may  be  justi- 

189 


190  THE  LIGHTING  ART 

fied  on  the  same  basis  as  their  existence  is  justified,  namely, 
to  beautify  the  world  in  which  we  live.  Of  course,  there  are 
other  aspects  of  flood-lighting  which  are  purely  utilitarian. 

On  looking  backward  only  a  few  years  we  see  a  sudden  de- 
parture from  the  old  scheme  of  outline  lighting  by  means  of 
incandescent  lamps  to  the  new  method  of  flooding  the  object 
with  light  from  projectors  or  concealed  units.  In  the  former 
method  the  object  was  not  made  visible  in  general,  for  the  effect 
seen  was  that  of  a  pattern  of  light-sources.  This  method  has 
been  largely  superseded  by  the  more  practicable  and,  in  general, 
more  satisfactory  method  of  flood-lighting;  however,  there  are 
still  many  applications  for  outline  lighting,  especially  when  the 
patterns  of  light-sources  are  combined  in  a  decorative  manner 
with  signs  studded  with  lamps  or  with  other  decorative  effects 
such  as  festoons  of  lamps.  The  wiring  difficulties  are  generally 
much  greater  than  those  attending  the  modern  flood-lighting 
installation. 

The  next  step  in  the  evolution  of  the  lighting  of  exteriors  was 
to  conceal  the  light-sources  along  cornices  and  behind  other 
projecting  parts.  The  effect  of  such  " concealed"  lighting  is 
often  very  satisfactory  for,  compared  with  outline  lighting  by 
means  of  exposed  light-sources,  it  is  often  more  pleasing  because 
at  least  a  portion  of  the  architectural  pattern  is  visible.  The 
next  step  was,  logically,  to  flood  the  entire  exterior  with  light 
or  at  least  to  illuminate  prominent  portions  of  it  such  as  a  dome 
or  tower.  As  a  consequence,  during  the  past  few  years  flood- 
lighting has  revealed  the  beauties  of  such  works  of  art  as  the 
Statue  of  Liberty,  the  Woolworth  Tower,  the  National  Capitol 
building,  and  the  entire  exterior  of  the  Panama-Pacific  Exposi- 
tion. In  the  last  case  and  in  others  of  minor  importance,  color- 
effects  have  played  an  important  part. 

But  flood-lighting  has  not  been  confined  to  the  lighting  of 
architectural  works  for  it  has  been  applied  to  pageantry,  to  the 
lighting  of  stained  glass  windows,  to  entire  grounds  such  as 
parks,  and  among  the  earliest  successful  attempts  the  Niagara 
Falls  was  flooded  with  light.  Those  who  witnessed  the  light- 
ing of  this  natural  wonder  will  perhaps  find  it  easy  to  justify 
the  employment  of  flood-lighting  purely  as  a  source  of  pleasure. 


SPECTACULAR  LIGHTING  191 

As  the  cost  of  lighting  decreases,  it  appears  safe  to  conclude 
that  the  applications  of  flood-lighting  will  greatly  increase. 

The  so-called  searchlight  has  been  a  prominent  factor  in  this 
field  of  lighting  but  with  the  recent  developments  in  incandes- 
cent filament  lamps  the  available  units  have  been  extended 
greatly.  There  are  now  available  a  large  number  of  projector 
units  varying  in  size  and  in  distribution  characteristic  from  a 
highly  concentrated  beam  to  one  of  considerable  spread.  When 
a  small  area  is  to  be  illuminated,  or  the  distance  from  the  unit 
to  the  object  is  large,  the  more  concentrating  units  are  generally 
the  proper  ones  to  use.  However,  if  it  is  necessary  to  place  the 
units  close  to  the  surface  to  be  illuminated,  a  beam  of  greater 
spread  is  usually  necessary.  There  should  be  no  difficulty  in 
choosing  the  proper  units  by  considering  the  manufacturer's 
data  in  connection  with  the  specific  conditions  of  the  problem. 

There  is  an  artistic  aspect  in  most  of  the  cases  of  flood-lighting 
which  should  be  considered.  Architecture  has  developed  under 
daylight  conditions  in  which  the  dominant  light  reaches  the 
object  from  above  the  horizontal  plane  of  the  object.  In  fact, 
an  angle  of  about  45  degrees  has  been  a  prominent  factor  in  the 
evolution  of  architectural  details.  Besides  this  it  should  be 
remembered  that  a  great  deal  of  light  reaches  the  shadows  both 
from  the  sky  and  by  reflection  from  surroundings.  For  these 
reasons  the  shadows  in  the  daytime  are  projected  in  a  general 
downward  direction  and  are  not  relatively  as  low  in  brightness 
compared  with  the  high-lights  as  under  artificial  lighting. 
Therefore,  if  it  is  the  aim  to  preserve  the  effect  which  the  archi- 
tect has  produced,  the  dominant  light  should  be  directed  from 
a  point  considerably  above  the  horizontal  plane  in  which  the 
objects  are  located.  For  example,  if  a  monument  is  to  be 
flood-lighted  with  the  aim  of  reproducing  the  daylight  effect  of 
light  and  shade  as  far  as  practicable,  the  dominant  light  should 
be  projected  from  a  point  sufficiently  high  so  that  the  angle  is 
from  30  to  45  degrees  above  the  horizontal  plane.  However, 
owing  to  the  scanty  amount  of  diffused  light  which  illuminates 
the  shadows  at  night  it  is  often  better  to  compromise  by  direct- 
ing the  light  more  nearly  horizontal  than  would  be  desired  if 
this  difficulty  were  not  encountered. 


192  THE  LIGHTING  ART 

Often  it  is  impossible  to  flood  the  object  with  light  except  by 
projecting  the  light  upward.  In  such  cases,  the  daylight  ap- 
pearance is  not  obtained  and  in  some  cases  the  effect  is  gro- 
tesque. However,  in  many  cases  the  effect  as  a  whole  is  striking 
and  attractive.  This  is  especially  true  if  there  are  no  conspicu- 
ously projecting  features  or  ornaments  on  the  exterior  but  in 
general  the  effect  is  more  satisfactory  when  the  light  reaches 
an  object  from  a  point  above  the  horizontal  plane  of  the  object. 
The  selection  and  location  of  the  units  are  largely  engineering 
problems  although  the  artistic  aspect  should  be  borne  in  mind 
when  considering  their  location. 

One  of  the  greatest  advantages  of  the  flood-lighting  unit  is 
that  the  distance  from  which  a  given  area  may  be  highly  illu- 
minated is  greatly  increased  over  that  at  which  an  ordinary 
reflector  may  be  employed.  The  latter  may  be  located  close 
to  a  billboard,  a  stained  window,  or  building  exterior  and  the 
results  are  quite  satisfactory.  However,  a  concentrating  pro- 
jector may  be  placed  several  hundred  feet  from  the  top  of  a 
chimney,  tower,  or  monument  and,  owing  to  the  high  flux- 
density  of  the  beam,  the  object  may  be  highly  illuminated. 
For  example,  the  top  of  the  Washington  Monument  has  been 
illuminated  from  a  distance  of  hundreds  of  feet  and  the  effect 
is  very  attractive  and  even  mysterious.  Signs  painted  on 
chimneys  and  towering  spires  are  illuminated  very  satisfactorily 
in  this  manner.  One  of  the  prettiest  effects  is  obtained  from 
a  projector  located  on  top  of  a  chimney  which  emits  smoke  or 
steam  by  projecting  the  light  upward.  Thus  the  smoke  or 
steam  is  illuminated  and  owing  to  its  changing  pattern  the 
effect  is  beautiful  especially  if  a  tinted  color-screen  is  used. 
One  disadvantage  is  that  such  illumination  unduly  advertises 
the  undesirable  smoking  chimney,  nevertheless  the  idea  may  be 
applied  in  many  cases,  especially  in  connection  with  a  sign  at 
the  top  of  the  chimney. 

An  example  of  this  effect  on  a  large  scale  is  the  scintillator 
originated  by  W.  D'A.  Ryan  who  employed  a  battery  of 
powerful  searchlights  and  jets  of  steam.  These  beams,  which 
were  arranged  in  a  fan-like  manner,  illuminated  the  clouds  of 
steam  in  a  spectacular  manner.  When  equipped  with  colored 


SPECTACULAR  LIGHTING  193 

screens  the  effect  is  very  beautiful.  On  foggy  nights  such  an 
effect  is  commonly  witnessed  when  searchlights  are  in  use. 
Ryan  has  employed  artificial  " clouds"  on  various  occasions 
with  excellent  results. 

The  effects  obtained  by  illuminating  fountains  are  not  far 
removed  from  those  obtained  with  other  mobile  media  such  as 
steam  and  smoke.  Illuminated  fountains  and  cascades  have 
been  attractive  and  spectacular  features  of  some  of  the  large 
expositions  and  many  interiors  and  exteriors  have  been  beauti- 
fied by  using  flashing  colored  lights  for  illuminating  small 
fountains.  Such  installations  are  not  difficult  to  make  especi- 
ally if  planned  in  advance  of  the  construction.  If  gelatine 
color-screens  are  employed  it  is  essential  to  provide  an  easy 
means  for  renewing  them.  The  selection  of  the  colors  is  a 
matter  of  taste  but  it  is  usually  more  satisfactory  to  employ 
tints  than  the  purer  colors.  A  checkerboard  color-screen  made 
up  of  small  and  irregular-shaped  pieces  of  colored  media  may 
be  used  to  advantage.  The  mixing  of  the  colors  by  refraction 
and  reflection  in  the  moving  water  adds  a  liveliness  and  variety 
which  may  be  very  attractive  if  done  properly.  In  such  effects 
rheostatic  control  is  often  a  desirable  feature.  The  units  may 
be  immersed  in  water-tight  compartments  or  the  light  may  be 
projected  from  above  if  desired. 

The  lighting  of  the  Panama-Pacific  Exposition  was  an  excel- 
lent example  of  the  use  of  various  modern  illuminants  and  many 
special  light-sources  and  color-screens  in  a  spectacular  effect 
of  large  magnitude.  In  such  effects  the  flicker  of  electric  arcs 
and  gas  lamps  is  often  attractive.  At  this  exposition  a  system 
of  masked  flood  and  relief  lighting  was  generally  employed.  The 
intensities  of  illumination  ranged  from  o.i  to  3  foot-candles  on 
roadways  and  building  facades  and  from  5  to  15  foot-candles 
on  certain  points  of  interest  such  as  towers,  flags,  and  sculptural 
groups.  The  use  of  " jewels"  on  the  Tower  of  Jewels  is  well 
known  and  the  myriads  of  scintillating  reflected  lights  viewed 
against  the  dark  sky  was  a  fitting  climax  of  spectacular  and 
gorgeous  beauty.  No  brief  discussion  can  do  justice  to  the 
magnificent  spectacle  of  lighting  at  this  exposition,  so  the  reader 
is  referred  to  descriptions  of  the  installations  and  effects  ob- 


194  THE  LIGHTING  ART 

tained  as  presented  by  W.  D'A.  Ryan  who  conceived  and 
executed  the  plans  for  this  greatest  achievement  in  spectacular 
lighting. 

There  are  many  opportunities  for  spectacular  and  attractive 
lighting  on  a  small  scale  in  which  the  possibilities  of  strik- 
ing distributions  of  light  and  color-effects  may  be  employed. 
It  is  strange  that  advantage  of  these  possibilities  has  not  been 
grasped  more  fully  in  advertising.  For  example,  a  simple  scenic 
sign  in  color  may  be  made  a  great  deal  more  striking  by  the  use 
of  colored  illuminants.  Mobile  color-effects  may  be  pro- 
duced readily  by  varying  the  color  of  the  light  in  a  desired  se- 
quence by  means  of  motor-driven  rheostats,  flashers,  or  tem- 
plates. In  such  a  case,  dawn,  noon,  sunset,  and  moonlight 
effects  may  be  obtained  in  a  proper  sequence  in  the  course  of 
a  few  minutes  with  the  result  that  the  sign  is  of  much  greater 
value  as  an  advertising  medium.  It  is  well  known  that  such 
variations  in  intensity  and  in  color  draw  the  attention  of  many 
more  persons  than  if  the  intensity  and  color  of  the  light  were 
constant.  The  color-effects  may  be  obtained  from  units  sup- 
ported in  front  or  the  sign  may  be  recessed  in  a  manner  similar 
to  a  shallow  stage.  In  the  latter  case  the  light-sources  may  be 
installed  behind  opaque  screens  such  as  are  employed  on  the 
stage. 

Mobile  color-effects  may  be  obtained  in  a  variety  of  ways. 
One  of  the  most  complete  and  effective  schemes  is  to  employ 
red,  green,  and  blue  lamps  whose  intensities  are  controlled  by 
means  of  rheostats.  An  apparatus  for  such  a  purpose  may  be 
made  as  indicated  in  Fig.  40.  A  series  of  contacts  are  placed 
on  the  circumference  of  a  cylinder  as  shown  and  these  are  points 
on  a  continuous  resistor  of  the  proper  current-carrying  capacity 
and  resistance  depending  upon  the  wattage  of  lamps  to  be  used. 
Two  arms,  #,  attached  rigidly  together,  are  connected  to  one 
side  of  the  line  and  are  rotated  by  means  of  a  small  motor.  The 
red,  green,  and  blue  lamps  are  connected  as  shown  and  by  this 
means  the  spectral  colors  may  be  produced  in  their  proper  order 
with  purple  spanning  the  gap  between  blue  and  red.  The 
sequence  is  as  follows:  red,  orange,  yellow,  green,  blue-green, 
blue,  blue-purple,  purple,  red-purple,  etc.  The  modifications 


SPECTACULAR  LIGHTING 


195 


which  must  be  made  in  this  apparatus  for  producing  other  de- 
sired sequences  of  colors  should  be  obvious. 

The  same  effect  may  be  produced  with  water  rheostats  by 


LINE 


FIG.  40. — Apparatus  for  mixing  red,  green,   and  blue  lights  for  mobile-color 

effects. 

operating  plungers  by  means  of  cams  or  eccentrics.  Such  a 
scheme  is  indicated  in  Fig.  41,  where  V  is  a  vessel  filled  with 
salt  water,  P  is  a  plate  connected  to  one  side  of  the  line,  R  is  a 


LINE 


FIG.  41. — A  simple  rheostat   which  is   adaptable  to  mixing  colored  lights  by 
varying  their  intensities. 

metal  rod  connected  to  the  other  side  of  the  line,  L  are  incan- 
descent lamps,  G  are  guides  for  the  rod  which  is  kept  in  contact 
with  the  eccentric  E  by  means  of  a  helical  spring.  Several 


196  THE  LIGHTING  ART 

mechanisms  of  this  sort  may  be  operated  from  the  same  shaft 
S  and  by  varying  the  design  and  angular  position  of  the  eccen- 
trics or  cams  various  effects  may  be  produced.  The  various 
dimensions  and  other  features  may  be  determined  readily  by 
experiment  for  a  particular  case. 

As  mentioned  in  another  chapter,  templates,  color-wheels, 
color-mixers,  etc.,  provide  other  means  for  obtaining  mobile 
color-effects.  Many  places  are  found  in  lighting  for  such  ap- 
paratus even  on  a  small  scale.  Among  these  are  signs,  dis- 
plays, show-windows,  fountains,  the  stage,  etc.  A  vast  amount 
of  ingenuity  may  be  expended  upon  the  electric  sign  in  order 
to  develop  all  of  the  possibilities  of  this  field  of  spectacular 
lighting. 

Spectacular  effects  are  merely  the  result  of  applying  well- 
known  facts  of  optics  and  the  possibilities  are  so  extensive  and 
depend  so  much  upon  the  particular  case  that  little  more  can  be 
done  in  a  brief  chapter  than  to  describe  a  few  cases  and  to  make 
a  few  suggestions.  Many  of  the  simple  facts  of  light,  shade  and 
color  have  been  discussed  in  preceding  chapters  and  have  been 
treated  extensively  elsewhere  so  that  those  who  meet  such 
problems  should  be  able  to  solve  them.  The  more  important 
fact  is  that  lighting  specialists  are  overlooking  opportunities 
daily  for  tapping  the  potentiality  of  lighting.  On  every  hand 
such  opportunities  are  to  be  found  but  it  is  necessary  to  exercise 
ingenuity  and  imagination  in  utilizing  light  in  this  manner. 
There  is  some  apparatus  available  but  usually  it  is  necessary 
to  devise  it  for  a  specific  case.  For  this  reason  the  subject 
cannot  be  treated  briefly  and  to  do  it  full  justice  by  discussing 
the  many  details  elaborately  is  quite  beyond  the  scope  of  this 
small  volume. 


CHAPTER  XXII 
COMPUTATIONS  AND  DATA 

The  viewpoint  expressed  in  this  book  is  that  lighting  should 
be  considered  much  more  broadly  than  is  usually  done  in  aiming 
merely  to  provide  a  certain  more  or  less  empirical  intensity  of 
illumination  on  a  horizontal  "work-plane."  For  this  reason 
considerable  stress  has  been  laid  upon  the  distribution  and  color 
of  light  over  the  entire  room  which  includes  walls,  ceiling,  and 
the  various  objects  as  well  as  the  floor.  Furthermore,  the  prob- 
lem of  lighting  should  be  considered  as  being  closely  allied  or 
even  synonymous  to  vision;  therefore  various  planes  and  even 
the  details  of  seeing  should  be  reckoned  with  in  most  lighting 
problems.  It  is  also  necessary  to  distinguish  between  illumina- 
tion and  brightness — respectively,  cause  and  effect — and  it  is 
thus  seen  that  the  color  and  reflection-factors  of  backgrounds 
and  of  the  various  elements  of  decorative  schemes  must  be 
considered. 

Few  working  rules  are  available  which  may  be  depended  upon 
at  the  present  time  for  designing  lighting  installations  from  this 
broader  view  which  aims  to  do  justice  to  the  potentiality  of 
light  and,  therefore,  the  lighting  specialist  must  draw  upon 
various  sources  of  information  and  through  imagination,  experi- 
ment, and  experience  he  should  be  able  to  utilize  light  in  lighting 
effects  in  a  manner  similar  to  that  of  the  painter  whose  media 
are  pigments.  A  great  amount  of  lighting  may  be  done  very 
well  without  resorting  to  computations.  In  fact  much  of  the  pres- 
ent practice  is  the  result  of  experience  and  judgment  in  which 
computations  are  practically  impossible  or  unnecessary.  How- 
ever, in  many  cases  it  is  necessary  to  have  a  certain  illumination 
intensity  on  the  floor  or  on  an  imaginary  plane  somewhat 
above  it.  By  choosing  the  proper  lighting  equipment  the 
desired  general  effect  may  be  obtained  and  by  computation  the 
required  luminous  output  of  each  unit  may  be  determined. 

197 


198  THE  LIGHTING  ART 

Uniformity  of  illumination  is  another  factor  which  is  often 
important.  This  is  usually  a  matter  of  properly  relating  the 
spacing  and  mounting  height  of  the  lighting  units  which  are 
chosen.  For  example,  if  direct-lighting  units  of  broad  or  ex- 
tensive distribution  are  chosen  it  is  obvious  that  they  may  be 
hung  higher  from  the  "work-plane"  or  spaced  farther  apart 
than  if  concentrating  or  focusing  units  were  selected.  The 
relation  between  mounting-height  and  spacing-distance  is 
purely  geometrical  and  it  is  possible  to  establish  relations  for 
various  general  types  of  units  which  will  yield  satisfactory 
results  in  practice.  A  few  data  of  this  character  are  presented 
in  the  accompanying  table  in  which  mounting-height  is  the 
vertical  distance  between  the  horizontal  plane  under  con- 
sideration and  that  of  the  units.  In  the  case  of  indirect  and 
so-called  semi-indirect  lighting,  the  mounting-height  is  the 
vertical  distance  between  the  "  work-plane  "  and  the  ceiling,  the 
latter  being  considered  to  be  the  light-source. 

RELATION  BETWEEN   SPACING  AND    MOUNTING-HEIGHT  FOR   APPROXIMATELY 
UNIFORM  ILLUMINATION  ON  A  HORIZONTAL  PLANE 


Equipment 

Spacing-distance 
M  ounting-height 

Prismatic, 
mirrored, 
or  aluminized 
reflectors 
Opal  bowls 

f  Focusing  .... 
s  Intensive  .... 
[  Extensive  .  .  . 

H 

iM 

2 

1% 
1% 
1% 

i« 

ifc 

Opal  domes 

Enclosing  glass 
Semi-indirect  u 
Indirect  units.. 

units  

[nits    . 

For  example,  suppose  a  large  office  is  to  be  provided  with  an 
approximately  uniform  intensity  of  illumination  on  the  plane  of 
the  desk  tops,  2.5  feet  above  the  floor'.  Assume  that  the  ceiling 
is  15  feet  above  the  floor  and  that  extensive  prismatic  re- 
flectors appear  to  be  the  most  desirable  equipment  for  this  case. 
It  is  well  to  hang  units  high;  therefore  10  feet  will  be  chosen 
as  the  mounting-height.  The  spacing  will  be  found  by  mul- 
tiplying the  ratio  2,  from  a  previous  table,  by  the  mounting- 


COMPUTATIONS  AND  DATA  199 

height,  10.  The  result  is  20  feet  between  units.  In  many 
offices  of  these  dimensions  either  semi-indirect  or  indirect 
lighting  is  quite  satisfactory.  If  such  units  are  desired,  the 
spacing  will  be  found  by  multiplying  the  ratio  1.5  by  12.5. 
The  result  is  approximately  19  feet  between  units. 

The  intensity  of  illumination  which  is  acceptable  for  a  certain 
activity  or  condition  is  largely  a  matter  of  opinion  or  of  experi- 
ence inasmuch  as  satisfactoriness  must  be  the  guiding  factor  in 
the  absence  of  direct  methods  of  determination.  If  any  criti- 
cism may  be  directed  at  the  intensities  of  artificial  illumination 
which  are  found  in  practice  at  the  present  time  they  will 
generally  be  safely  criticized  as  being  too  low.  If  the  light- 
sources  are  properly  diffused  and  if  brightness-contrasts  are 
not  too  high  there  appears  to  be  no  reason  except  that  of 
economy  for  not  employing  intensities  of  illumination  many 
times  greater  than  those  ordinarily  encountered.  The  inten- 
sities of  daylight  are  ordinarily  much  higher  than  those  con- 
sidered sufficiently  great  for  artificial  light.  The  daylight 
intensities  range  as  high  as  10,000  foot-candles  outdoors  on  a 
clear  day  and  it  is  not  unusual  to  find  intensities  indoors  of 
hundreds  of  foot-candles.  However,  we  appear  to  be  content 
with  an  illumination  indoors  of  a  few  foot-candles  of  artificial 
light. 

The  eye  is  a  wonderfully  adaptable  organ  for  it  adjusts  itself 
for  ranges  of  intensity  of  illumination  and  of  brightness  repre- 
sented by  millions.  That  is,  we  are  able  to  see  well  under 
daylight  intensities  outdoors  of  thousands  of  foot-candles  and 
fairly  well,  when  the  eye  is  properly  adapted,  under  intensities 
of  thousandths  of  a  foot-candle.  In  other  words,  the  eye  is 
capable  of  recording  brightnesses  extending  over  an  enormous 
range  in  value.  Perhaps  no  instrument  constructed  by  man 
has  a  range  of  sensibility  comparable  with  that  of  the  eye; 
however,  it  appears  reasonable  not  to  depend  too  much  upon 
this  wonderful  flexibility  of  the  visual  organs.  The  ability  of 
the  eye  to  distinguish  minute  details,  brightness  differences, 
hue  differences,  flicker,  etc.,  is,  in  each  case,  a  function  of  the 
illumination  or  brightness  and  in  many  cases  appears  to  be 
directly  proportional  to  the  logarithm  of  the  brightness. 


200  THE  LIGHTING  ART 

For  this  reason,  there  is  little  difference  in  the  sensibility  of 
the  eye  to  these  factors  over  a  wide  range  of  illumination  or 
brightness;  however,  at  low  illuminations  or  brightnesses  the 
sensibility  generally  decreases  rapidly.  Although  there  is  no 
definite  brightness  at  which  the  eye  begins  to  function  differ- 
ently, it  may  be  safe  to  state  that  a  general  decrease  in  sensibility 
and  change  in  the  functions  of  the  eye  begins  to  be  evident 
at  brightnesses  corresponding  to  that  of  a  white  surface  under 
an  illumination  of  o.i  foot-candle.  This  corresponds  to 
brightnesses  of  objects  of  lower  reflection-factors  under  illu- 
minations of  higher  intensities.  In  fact,  from  this  view  of  the 
physiology  of  vision  it  appears  reasonable  to  state  that  in  order 
to  be  safe  the  intensities  of  artificial  light  should  be  generally 
raised  so  that  nobody  is  obliged  to  work  constantly  under 
intensities  of  illumination  less  than  a  few  foot-candles.  This 
may  appear  to  be  a  radical  view  but  in  the  absence  of  more 
definite  data  it  is  at  least  a  safe  one  and  it  will  not  be  surprising 
if,  eventually,  it  were  proved  that  much  of  the  criticism  of 
artificial  lighting  is  due  to  the  low  intensities  employed. 

A  table  is  given  of  the  intensities  of  illumination  which  are 
generally  considered  as  acceptable  practice  at  the  present  time 
for  various  activities.  These  values  should  be  viewed  in  the 
light  of  the  foregoing  discussion  and  should  be  considered  as 
being  merely  tentative  values  subject  to  change  as  our  knowl- 
edge of  this  phase  of  lighting  increases.  In  specifying  intensi- 
ties of  illumination  for  various  activities  which  are  practised 
in  the  same  room  or  in  adjoining  rooms  the  local  conditions 
must  be  considered.  For  example,  a  rather  low  value  of 
illumination  is  given  for  storage  rooms;  however,  if  operators 
are  obliged  often  to  leave  a  highly  illuminated  room  to  enter  this 
storage  place  it  would  be  better  to  supply  a  higher  intensity 
for  the  latter  space  in  order  to  avoid  the  discomfort  and  loss 
of  time  required  in  adapting  the  eyes  to  this  extreme  difference 
in  the  two  levels  of  illumination.  Consideration  of  such  factors 
of  vision  results  in  proper  lighting  and  distinguishes  the  light- 
ing specialist  from  those  who  merely  follow  empirical  rules  which 
cannot  possibly  cover  the  varying  condition  found  in  practice. 

The  computation  of  illumination  intensity  is  easy  in  simple 


COMPUTATIONS  AND  DATA 


201 


cases  but  in  the  complex  cases  of  practice  where  light  arrives 
at  a  given  point  from  many  light-sources  and  by  reflection 
from  many  objects  it  is  quite  impossible  to  compute  the  in- 
tensity of  illumination  at  the  given  point.  For  this  purpose 
various  factors,  such  as  coefficients  of  utilization  for  various 
general  conditions,  are  experimentally  determined  and  these 
are  used  in  computations.  Before  discussing  these  it  appears 
of  interest  to  treat  the  simple  case.  In  Fig.  42,  S  is  a  small 
surface  perpendicular  to  the  line 
joining  its  center  with  the  light- 
source.  If  the  luminous  intensity 
or  candlepower  of  the  light-source 
is  I  in  the  direction  of  a  given  sur- 
face, and  the  distance  from  the 
source  to  the  surface  S  is  equal  to 
d  in  feet  the  illumination  E  of  the 
surface  in  foot-candles  is  rep- 
resented by 

I  FIG.  42. — Illustrating  laws  of 

E  =  ~™  illumination. 

This  is  the  "inverse  square"  law  so  common  in  physics  and  is 
used  in  photometry  very  considerably.  In  general  the  surface 
is  not  normal  or  perpendicular  to  the  line  joining  it  and  the 
light-source.  Assume  it  to  be  in  the  position  Sr  and  the  angle 
between  the  normal  to  the  surface  ^V  and  the  direction  toward 
the  light-source  to  be  a;  then  the  illumination  in  foot-candles  or 
flux-density  on  the  surface  S'  is  represented  by 

I  cos  a 

=  — //2 — 

In  other  words,  as  the  angle  of  incidence  a  increases  the  flux- 
density  on  the  surface  decreases,  the  latter  being  a  maximum 
where  a  equals  zero  and  a  minimum  (zero)  where  a  equals  90 
degrees. 

The  foregoing  also  represents  the  definition  of  a  foot-candle 
which  is  the  illumination  on  S  when  the  distance  to  the  source 
is  i  foot  and  the  luminous  intensity  of  the  source  in  the  direc- 


202  THE  LIGHTING  ART 

tion  of  5  is  equal  to  i  candle.  The  latter  unit  is  an  arbitrary 
standard  adopted  and  maintained  by  the  national  laboratories 
of  several  countries  including  the  United  States. 

Inasmuch  as  the  luminous  intensity  of  light-sources  varies 
in  general  in  different  directions,  the  mean  horizontal  candle- 
power  has  been  extensively  used  as  a  means  of  comparing  the 
luminous  intensities  of  light-sources.  In  some  cases,  such  as 
in  street  lighting,  the  light  emitted  below  the  horizontal  has 
been  considered  the  useful  light  and  therefore  the  mean  lower 
hemispherical  candlepower  has  been  used  to  some  extent  for 
comparing  light-sources  and  lighting  units.  Another  step  was 
taken  in  averaging  the  candlepower  of  a  lamp  in  all  directions 
and  this  is  called  the  mean  spherical  candlepower  of  the  lamp. 
Although  of  these  various  measurements  of  luminous  intensity 
or  candlepower  the  last  is  the  most  serviceable  none  of  these 
gives  an  indication  of  the  total  quantity  of  light  emitted  by  a 
source.  Candlepower  in  a  given  direction  corresponds  to  a 
measurement  of  the  depth  of  a  pond  of  water  at  a  certain  point 
but  gives  no  indication  of  the  quantity  of  water  in  the  pond. 

Thus  it  is  seen  that  a  unit  is  necessary  in  terms  of  which  the 
quantity  of  light  emitted  by  a  source  may  be  measured.  For 
this  purpose  the  lumen  has  been  adopted  as  the  unit  of  luminous 
flux  and  it  is  equal  to  the  flux  emitted  in  a  unit  solid-angle  (a 
steradian)  by  a  point-source  of  i  candlepower.  There  are  4?r 
unit  solid-angles  radiating  from  a  point  in  space  so  that  a 
point-source  having  a  luminous  intensity  of  i  candle  in  all 
directions  or  a  mean  spherical  candlepower  of  i  candle,  emits 
47r  lumens.  The  luminous  output  of  any  source,  expressed  in 
lumens,  is  equal  to  the  mean  spherical  candlepower  multiplied 
by  47r  which  is  approximately  equal  to  12.57. 

This  may  be  made  more  clear  by  referring  to  Fig.  43  in  which  a 
source  having  a  luminous  intensity  of  i  candle  in  all  directions 
is  assumed.  Suppose  an  imaginary  sphere  having  a  radius  of  i 
foot  envelops  the  source  which  is  at  the  center.  If  this  sphere  is 
perfectly  black  inside,  only  light  coming  directly  from  the  source 
will  escape  from  any  opening  such  as  OO.  The  quantity  of  light 
which  escapes  will  vary  directly  as  the  area  of  the  opening, 
however  a  point  at  a  certain  place  along  the  line  H  will  have  a 


COMPUTATIONS  AND  DATA 


203 


constant  illumination  regardless  of  the  size  of  the  opening 
assuming  the  source  to  be  confined  to  a  relatively  small  area. 
This  shows  that  the  illumination  at  a  given  point  depends  upon  the 
candlepower  in  its  direction  but  of  course  the  distance  to  this 
certain  point  is  also  a  factor  as  already  shown. 

If  the  quantity  of  light  (luminous  flux)  which  escapes  from 
this  blackened  sphere  depends  upon  the  area  of  the  opening  it 
is  obvious  that  we  have  a  means  of  establishing  a  unit  of 
luminous  flux.  If  the  area  of  the  opening  is  taken  as  i  square 


FIG.  43. — Illustrating  luminous  output  (lumens)  and  its  relation  to  luminous 

intensity  (candles). 

foot  and  the  radius  of  the  sphere  is  equal  to  i  foot,  i  lumen  of 
flux  will  escape.  This  solid-angle  will  remain  the  same  for 
any  sphere  if  the  proportions  are  kept  the  same  and  thus  serves 
as  a  unit  solid-angle.  There  are  471-  or  12.57  square  feet  on  the 
surface  of  this  sphere  of  i  foot  radius  and  therefore  there  are 
47r  solid-angles  surrounding  the  center.  Furthermore,  there 
are  then  4?r  lumens  emitted  by  this  point-source  of  i  mean 
spherical  candlepower  as  has  been  stated  above. 

It  is  obvious  if  the  point  source  has  a  luminous  intensity 
of  5  candles  in  all  directions,  that  there  will  be  five  times  as 
much  light  emitted  by  a  given  area  of  an  imaginary  spherical 
envelope  or  by  a  given  solid-angle.  It  is  easy  to  see  from  the 
foregoing  that  the  intensity  of  illumination  on  the  sphere  in 
Fig.  43  is  i  foot-candle,  hence  the  intensity  of  illumination  of 


204 


THE  LIGHTING  ART 


a  surface  in  foot-candles  is  numerically  equal  to  the  lumens 
incident  upon  the  surface. 

Recently  there  has  been  a  general  acceptance  of  the  lumen 
and  the  luminous  output  of  lamps  and  of  lighting  units  is  being 
expressed  in  lumens.  In  fact,  the  introduction  of  the  lumen 
has  resulted  in  a  more  rational  method  of  dealing  with  luminous 
flux.  In  computations  it  is  essential  .to  know  that  for  every 
foot-candle  of  intensity  per  square  foot  of  a  given  plane,  i 
effective  lumen  is  required.  However,  it  is  impossible  to  com- 
pute the  amount  of  light  contributed  to  a  certain  point  by 
reflections  from  various  surfaces  in  a  room  so  that  computations 
must  be  based  upon  the  general  results  of  experiment.  For  this 
purpose  the  coefficient  of  utilization  is  used.  This  is  the  ratio 
of  the  lumens  which  reach  the  horizontal  " work-plane"  30 
inches  above  the  floor  to  the  total  lumens  emitted  by  the 
primary  light-sources.  Obviously  the  coefficient  of  utilization 
will  depend  upon  the  nature  of  the  lighting  unit  and  upon  the 
reflection-factors  of  walls  and  ceiling.  In  the  accompanying 
table  such  data  are  presented  for  three  types  of  lighting  systems, 
and  for  three  sizes  of  rooms,  for  two  different  combinations  of 
reflection-factors  of  walls  and  ceiling. 

APPROXIMATE  COEFFICIENTS  OF  UTILIZATION1 
(Modern  Lighting  Equipment  with  no  Allowance  for  Depreciation) 


* 

Ceiling—  nearly 
white  ;    walls  — 
high    reflection- 
factor 

Ceiling  —  nearly 
white  ;    walls  — 
medium  reflec- 
tion factor 

Small  Rooms  (Offices,  corridors,  etc.) 
Direct  lighting;  dense  glass. 

Per  cent. 

A.O 

Per  cent. 
^6 

Semi-indirect  lighting;  dense  glass  
Indirect  lighting;  mirrored  glass 

25 

27 

22 

20 

Medium  rooms  (Classrooms,  laboratories,etc.) 
Direct  lighting;  dense  glass  
Semi-indirect  lighting;  dense  glass. 

48 

•32 

45 
20 

Indirect  lighting;  mirrored  glass.. 

20 

26 

Large  rooms  (Auditoriums,  assembly  rooms, 
etc.) 
Direct  lighting;  dense  glass. 

60 

S8 

Semi-indirect  lighting;  dense  glass  

47 

41 

Indirect  lighting;  mirrored  glass  

40 

38 

1  Determined  by  Engineering  Department,  National  Lamp  Works  of  General 
Electric  Company. 


COMPUTATIONS  AND  DATA  205 

ILLUMINATION   INTENSITIES   WHICH  ARE  ACCEPTABLE  AT  THE  PRESENT  TIME 

Foot-candles 

Churches,  theatres,  lodge  rooms i .  5-3 .  o 

Gymnasiums 1-5 

Armories,  public  halls  2-4 

Libraries 3-6 

Schools:  classrooms,  study-rooms,  libraries,  laboratories 3-6 

Show-windows  (depending  largely  upon  goods  displayed  and  in- 
tensity of  street  illumination) 10-50 

Accurate  color-discrimination 10-50 

Stores: 

Department,  dry  goods,  clothing,  furnishing,  millinery,  jewelry, 

etc * 5-10 

Drug,  florist,  furniture,  book,  grocery,  meat,  etc 3-6 

Offices 4-7 

Industries: 

Foundry,  rough  wood-working,  pottery,  baking 2-4 

Fine  wood-working,  rough  metal-working,  laundries,  canneries, 

paint,  paper,  textile,  printing,  forge 3-6 

Fine  metal- working,  cabinet-making,  jewelry,  garment,  shoe.  .  5-10 

Drafting,  sewing 8-12 

Storage,  passageways o .  25-1 .  oo 

Stairways 0.5  -2.0 

Packing  and  shipping 1-4 

Building  exteriors 3~*5 

It  follows  from  the  foregoing  discussion  that  the  lumens, 
L,  to  be  emitted  by  the  primary  light-sources  in  a  given  room 
of  floor-area  A  in  order  to  supply  an  average  intensity  of  illu- 
mination E  in  foot-candles  on  the  horizontal  work-plane,  is 
found  by  means  of  the  following  relation, 

AE 


L  = 


U 


where  U  is  the  coefficient  of  utilization.  Owing  to  accumula- 
tion of  dust  on  the  lamps  and  on  the  reflecting  and  diffusing 
surfaces  of  the  lighting  units  and,  owing  to  the  decrease  in  the 
luminous  output  of  lamps,  an  allowance  should  be  made  for 
depreciation.  This  allowance  is  so  variable  that  no  single 
value  would  be  equitable  for  all  cases;  however,  owing  to  the 
fact  that  the  illumination  intensity  E  is  not  a  rigid  requirement 
it  appears  safe  to  allow  a  depreciation  of  20  per  cent,  of  the 
initial  value. 
Assume  that  a  room,  20  by  30  feet,  is  to  be  provided  with  an 


206  THE  LIGHTING  ART 

intensity  of  illumination  of  5  foot-candles  on  a  horizontal 
work-plane  and  that  an  indirect  lighting  system  is  chosen  as 
most  suitable  for  the  given  case.  The  room  may  be  considered 
of  medium  size  and  if  the  walls  are  of  high  reflection-factor 
and  the  ceiling  is  white,  the  coefficient  of  utilization  is  found  in 
the  preceding  table  to  be  0.29.  The  total  lumens  required  from 
the  lamps  are  equal  to 

20  X  30  X  5  f  N 

=          ~OT2Q~  =    I0'3°°  (aPPrOX') 

p 

If  20  per  cent,  more  lumens  are  allowed  for  depreciation,  the 
total  lumens  required  will  be  approximately  12,360.  If  the 
ceiling  height  is  such  that  six  units  are  required  it  is  seen  that 
about  2060  lumens  must  be  generated  in  each  lighting  unit. 
The  size  of  the  individual  lamps  may  be  determined  from  the 
manufacturer's  data  and  from  other  considerations. 

Often  the  construction  of  the  room  and  the  decorative  scheme 
determine  the  locations  of  outlets  and,  therefore,  units  must  be 
selected  which  provide  the  desired  uniformity  and  intensity  of 
illumination  under  the  conditions.  In  fact,  it  is  seldom  that 
an  appropriate  lighting  installation  will  be  determined  by  blindly 
following  such  computations  as  presented  in  the  foregoing ;  how- 
ever, some  definite  basis  must  be  available  for  making  pre- 
liminary computations.  These  data  are  intended  for  such  a 
purpose. 

In  the  past  many  computations  were  made  on  the  basis  of 
watts  per  square  foot  of  floor-area  and  by  weighting  the  various 
obvious  factors  such  as  the  type  of  lighting  unit,  the  size  of  the 
room  and  the  reflection-factors  of  walls  and  ceiling.  For  in- 
stallations of  gas  units  a  corresponding  input-factor  was  used. 
However,  it  is  seen  that  such  a  basis  is  not  as  satisfactory  as 
the  lumen  basis  because  in  the  former  case  the  luminous  effi- 
ciency of  the  lamp  must  be  considered.  Now  that  manu- 
facturers are  rating  lamps  in  lumens  it  is  well  to  adopt  the  latter 
basis  for  computations. 

In  the  case  of  a  show-window  such  a  basis  as  lumens  per 
running  foot  of  the  window  provides  a  means  for  determining  the 
size  of  lamps  required.  In  the  case  of  tungsten  lamps  the 


COMPUTATIONS  AND  DATA  207 

computations  are  generally  made  on  the  basis  of  watts  per 
running  foot  because  the  general  practice  is  now  confined  largely 
to  certain  types  of  lamps  not  differing  greatly  in  wattage  and 
in  luminous  efficiency.  A  simple  rule1  for  Mazda  C  lamps 
is  to  divide  the  show-windows  into  classes  from  i  to  10,  class 
i  including  those  in  which  the  lowest  standard  of  illumination 
is  required  and  class  10  those  of  the  largest  stores  and  exclusive 
shops  on  brightly  lighted  streets.  Classes  5  and  6  cover  the 
average  store.  The  rule  is  to  add  the  depth  of  the  window, 
in  feet,  to  the  height  of  the  lamps  above  the  window  floor,  in 
feet,  and  to  multiply  this  sum  by  the  class  number  of  the 
window.  The  result  represents  the  watts  required  per  running 
foot  of  the  show-window  if  Mazda  C  lamps  are  used.  If 
Mazda  C-2  lamps  are  used  50  per  cent,  more  watts  are  re- 
quired for  approximately  the  same  intensity  of  illumination. 
Although  this  rule  will  provide  satisfactory  intensities  for  the 
type  of  window  considered,  it  appears  best  where  conditions 
permit  to  provide  three  or  four  interwoven  circuits  of  the 
character  of  the  one  determined  by  computation.  The  show- 
window  is  a  stage  and  should  be  provided  with  outlets  and  cir- 
cuits which  make  it  possible  to  produce  elaborate  lighting-effects 
when  they  are  desired. 

The  light-value  of  a  skylight  or  window  may  be  determined 
at  any  point  by  multiplying  the  area  of  the  window  through 
which  the  sky  is  visible  by  the  brightness  of  the  sky.  This 
gives  the  available  candlepower  of  the  window  considered  from 
a  given  point  and  this  is  then  divided  by  the  square  of  the  dis- 
tance to  the  given  point  to  obtain  the  foot-candle  intensity  of  the 
illumination  at  that  point.  Obviously,  this  value  will  usually 
differ  at  various  points  in  the  room  because  of  the  variation  in 
the  amount  of  sky-area  visible.  This  computation  does  not 
take  direct  sunlight  into  account  and  does  not  allow  for  the  light 
reflected  from  the  surroundings  to  the  point  under  considera- 
tion. However,  the  minimum  light- value  of  an  opening  is 
chiefly  of  interest  and  this  will  obtain  when  the  sky  is  heavily 
overcast.  A  fair  average  sky-brightness  may  be  taken  as 

1  Bulletin  28,  Engineering  Department,  National  Lamp  Works  of  General 
Electric  Company. 


208  THE  LIGHTING  ART 

approximately  i  lambert  or  2  candles  per  square  inch.  On 
stormy  days  this  will  be  reduced  to  a  much  lower  value  so  that 
0.5  candles  per  square  inch  is  a  minimum  brightness  which  it  is 
well  to  assume  in  such  computations. 

If  a  skylight  is  18  feet  above  the  " work-plane"  and  an  in- 
tensity of  illumination  of  10  foot-candles  is  desired  at  a  point  on 
this  plane  the  rough  computation  for  the  area  of  the  skylight 
will  be  as  follows,  assuming  a  sky-brightness  of  0.5  candles  per 
square  inch  or  72  candles  per  square  foot: 

10X18X18 

-  =  45  square  feet 

Inasmuch  as  this  skylight  is  horizontal  it  is  fair  to  assume 
that  at  all  points  on  the  work-plane,  sky  will  be  visible  through 
the  opening.  In  the  case  of  diffusing  glass  the  computation  is 
more  complicated  but  it  will  be  conducted  in  the  same  manner 
after  its  brightness  is  estimated.  This  may  be  arrived  at 
approximately  through  various  considerations  but  a  discussion 
of  these  is  beyond  the  scope  of  this  chapter. 

In  the  foregoing  the  important  rudiments  of  illumination 
computations  have  been  discussed  but  in  closing  it  is  well  to 
discuss  the  matter  of  brightness  which  is  really  the  effect  of 
illumination.  The  brightness  of  a  surface  depends  not  only 
upon  the  intensity  of  illumination  but  upon  the  reflection- 
factor  and  other  physical  characteristics  of  the  surface.  Bright- 
ness may  be  expressed  in  terms  of  luminous  intensity  per  unit 
of  area  of  the  surface  when  the  latter  is  perpendicular  to  the 
line  of  sight.  When  it  is  not  perpendicular  to  this  line,  the 
area  projected  on  such  a  plane  must  be  considered.  In  the  case 
of  a  perfectly  diffusing  surface  the  brightness  is  the  same  for 
any  angle  at  which  it  is  viewed  provided  other  conditions  re- 
main constant.  According  to  the  definition,  brightness  may  be 
expressed  in  terms  of  candles  per  square  inch,  per  square  foot, 
etc.  A  unit  of  brightness  which  is  coming  into  use  is  the 
lambert  which  is  the  brightness  of  a  perfectly  diffusing  surface 
radiating  or  reflecting  i  lumen  per  square  centimeter.  Al- 
though this  unit  has  some  advantages  it  is  not  always  convenient 
to  use  in  ordinary  computations  because  it  is  a  measure  of 


COMPUTATIONS  AND  DATA  209 

luminous  output  rather  than  of  lumnious  intensity.  Further- 
more, no  perfectly  diffusing  surfaces  exist  and  relatively  few  are 
found  in  practice  which  approach  this  ideal. 

Brightness  expressed  in  candles  per  square  inch  may  be 
reduced  to  lamberts  by  multiplying  by  0.4868. 

A  millilambert  is  one-thousandth  of  a  lambert. 

A  lumen  emitted  by  a  square  foot  of  a  perfectly  diffusing 
surface  is  responsible  for  a  brightness  of  the  surface  of  1.076 
millilambert. 

One  lambert  equals  2.054  candles  per  square  inch. 

From  these  values  it  is  easy  to  compute  the  brightness  of  a 
surface  which  is  nearly  perfectly  diffusing  provided 'the  reflec- 
tion-factor and  the  intensity  of  illumination  of  the  surface  are 
known.  For  example,  if  the  surface  were  perfectly  reflecting 
and  diffusing  each  lumen  incident  on  a  square  foot  of  area  would 
be  totally  reflected  and  from  the  foregoing  a  brightness  of 
1.076  millilambert  would  result  from  each  lumen  reflected  per 
square  foot.  However,  a  foot-candle  is  equal  to  i  lumen 
incident  per  square  foot  so  for  an  intensity  of  illumination  of 
10  foot-candles  the  brightness  of  this  ideal  surface  would  be 
10.76  millilamberts.  If  the  reflection-factor  were  0.6  instead  of 
unity,  under  this  intensity  of  illumination  its  brightness  would 
be  6.456  millilambert.  This  may  be  converted  into  other 
units  of  brightness  by  means  of  the  data  already  presented. 
Unfortunately,  these  computations  are  based  upon  the  special 
case  of  a  perfectly  diffusing  surface.  The  ordinary  case  is 
difficult  to  compute  and  actually  impossible  unless  the  reflec- 
tion characteristic  curve  of  the  surface  is  known,  which  is  not 
usually  the  case. 


CHAPTER  XXIII 
NATURAL  LIGHTING 

Although  natural  daylight  is  of  great  importance  to  the 
human  race  from  the  standpoint  of  lighting,  it  has  received 
little  consideration  in  this  volume  because  it  is  of  less  direct 
importance  to  the  lighting  specialist  than  artificial  light. 
Natural  lighting  does  not  possess  the  potentiality  that  artificial 
lighting  does  because  it  is  generally  less  readily  controlled  and 
adapted  to  the  problems.  Furthermore,  the  architect  has 
become  well  acquainted  with  the  means  for  admitting  daylight 
into  interiors  because  of  the  influence  of  such  openings  upon  the 
location  and  plans  of  a  building  and  of  the  necessity  for  pro- 
viding these  openings  during  construction.  In  some  classes  of 
buildings,  such  as  school  buildings,  modern  office  buildings 
and  modern  factories,  the  daylighting  is  being  done  perhaps  as 
well  as  is  practicable,  however,  the  lighting  specialist  may  often 
be  a  valuable  aid  to  the  architect. 

It  does  not  appear  advisable  to  present  a  discussion  of  the 
engineering  of  natural  lighting  because  of  the  lack  of  general 
interest  of  this  aspect  among  lighting  specialists;  however,  a 
broad  view  of  lighting  and  its  possibilities  cannot  be  had 
without  being  familiar  with  the  general  characteristics  of  day- 
light. Therefore,  it  appears  of  interest  to  discuss  natural 
lighting  outdoors  and  indoors  briefly. 

Daylight  is  a  very  indefinite  term,  for  the  distribution,  quality 
(spectral  character),  and  intensity  of  daylight  vary  momentar- 
ily, daily,  seasonally,  and  geographically.  In  fact,  the  most 
striking  feature  of  daylight  is  its  variability  and,  although  this 
is  often  annoying,  the  lack  of  monotony  is  one  of  the  attractive 
features  of  daylight.  We  may  learn  much  from  Nature  regard- 
ing lighting  and  the  lesson  gained  from  its  lack  of  monotony  is 
to  aim  at  variety  in  artistic  lighting. 

On  a  clear  day  there  is  a  highly  directed  light  from  the  sun 

210 


/    NATURAL  LIGHTING  211 

which  varies  in  intensity  from  zero  at  sunrise  to  a  maximum  at 
noon  and  to  zero  again  at  sunset.  Besides  this  there  is  the 
light  from  the  sky  which  is  directional  to  some  extent  but  is 
considered  highly  diffused  because  of  the  large  angular  area  of 
the  sky.  The  intensity  of  skylight  is  close  to  zero  at  dawn  but 
has  arisen  to  a  considerable  value  at  sunrise  and  is  fairly  con- 
stant throughout  a  large  portion  of  the  day.  The  brightness  of 
the  sky,  and  consequently  the  intensity  of  skylight,  depends 
upon  atmospheric  conditions.  Add  to  these  variables,  the  effects 
of  moving  clouds,  of  the  different  horizons  as  seen  from  various 
points  outdoors  and  indoors,  of  the  changing  cloak  of  Nature 
and  of  many  other  factors  and  it  is  seen  that  daylight  is  extremely 
variable  in  distribution. 

The  quality  or  spectral  character  of  daylight  is  also  quite 
variable  as  is  evidenced  by  the  colors  of  sunrise  and  sunset  and 
by  the  bluish  color  of  the  sky  as  compared  with  sunlight.  The 
latter  is  very  apparent  to  the  careful  observer  for  the  shadows 
on  a  clear  day  are  seen  to  be  quite  bluish  in  color  compared  with 
their  sunlit  surroundings.  On  overcast  days  the  color  of  day- 
light is  a  mixture  of  sunlight  and  skylight  quite  similar  to  their 
mixture  on  a  clear  day,  although  certain  atmospheric  conditions 
appear  to  be  responsible  for  changes  in  the  spectral  character 
of  the  light.  There  is  a  popular  belief  that  noon  sunlight  is 
yellow  in  color  but  this  is  due  largely  to  the  effect  of  hue  con- 
trast. For  example,  white  clouds  viewed  amid  the  surrounding 
blue  of  the  sky  appear  to  be  quite  yellow  in  color.  However,  if 
they  are  viewed  through  a  small  hole  in  a  black  card  or  dark 
box  so  that  no  surrounding  blue  sky  is  visible,  they  appear 
quite  white. 

It  is  well  known  that  north  rooms  appear  much  "colder" 
in  color  than  south  rooms  in  this  hemisphere  and  this  fact  is 
important  in  lighting.  The  coldness  is  usually  overcome  by  the 
decorative  scheme  which  is  additional  proof  that  the  latter  is 
closely  interwoven  with  lighting.  The  hygienic  value  of  sun- 
light is  also  recognized  and  therefore  the  location  of  certain 
rooms  in  school  buildings,  hospitals,  homes,  etc.,  should  de- 
pend upon  the  orientation  of  the  building. 

The  mixing  of  daylight  and  artificial  light  in  interiors  is  an 


212  THE  LIGHTING  ART 

important  feature  in  lighting  which  involves  both  the  distribu- 
tion and  color  of  the  two  illuminants. 

The  intensity  of  daylight  illumination  outdoors  ranges  from 
practically  zero  to  as  high  as  10,000  foot-candles.  On  very 
clear  days  when  the  atmosphere  has  been  freed  from  much  of 
the  solid  matter  which  has  been  suspended,  the  entire  hemi- 
sphere of  sky  contributes  from  10  to  20  per  cent,  of  the  total 
light  which  reaches  a  horizontal  surface.  Obviously,  the  por- 
tion of  the  total  light  contributed  by  the  sky  at  a  given  point  on 
a  clear  day  decreases  with  the  angular  extent  of  sky  which  is 
visible  from  the  given  point.  These  facts  are  of  importance 
both  from  the  standpoint  of  light  and  shade  effects  on  objects 
and  of  the  light- values  of  daylight  openings  into  interiors.  The 
brightnesses  encountered  outdoors  are  of  an  extremely  greater 
magnitude  than  those  found  under  artificial  lighting  conditions 
but  the  brightness-contrasts  outdoors  are  usually  less  than 
those  encountered  indoors  at  night. 

Nature's  landscapes  are  really  effects  of  light,  shade  and  color, 
and  inasmuch  as  there  are  an  infinite  number  of  lightings  avail- 
able, Nature  provides  a  storehouse  of  studies  for  the  lighting 
specialist  who.  hopes  to  become  familiar  with  the  psychological 
or  artistic  aspects  of  lighting.  It  is  interesting  to  note  the 
changes  which  a  given  natural  setting  outdoors  undergoes  as 
the  distribution  and  color  of  daylight  varies.  Nature  not  only 
provides  a  vast  variety  of  lightings  which  may  be  studied  profit- 
ably but  it  has  been  a  powerful  influence  in  the  evolution  of 
taste.  One  cannot  note  the  general  decorative  scheme  of  in- 
teriors with  their  darker  floors  and  walls  and  lighter  ceilings 
without  seeing  the  resemblance  to  Nature's  landscapes.  In 
the  latter  the  brightnesses  are  ordinarily  greatest  in  the  sky. 
In  other  words,  the  foreground,  middle  distance  and  sky  of  a 
landscape  are  similar  in  arrangement  of  " values"  to  the  most 
common  decorative  scheme  employed  in  interiors.  However, 
variety  is  a  keynote  in  Nature's  lighting  which  it  is  well  to  bear 
in  mind  in  artificial  lighting. 

Among  all  the  lighting  lessons  which  Nature  teaches  there  is 
the  fundamental  one — the  rainbow — which  is  a  demonstration 
on  a  huge  scale  that  light  ordinarily  consists  of  many  individual 


NATURAL  LIGHTING  213 

rays  of  different  wave-lengths  which,  when  permitted  to  stimu- 
late the  visual  organs  separately,  produce  sensations  of  light 
differing  in  color.  In  other  words,  the  rainbow  is  a  natural 
decomposition  of  sunlight  into  its  component  rays.  In 
the  study  of  light  and  color  a  similar  separation  of  the 
spectral  colors  is  made  by  means  of  the  prism  or  diffraction 
grating. 

Few  attempts*  have  been  made  to  modify  the  daylight  which 
enters  buildings  but  there  appear  to  be  possibilities  in  this  direc- 
tion. An  incandescent  source  such  as  the  sun  emits  radiant 
energy  which  when  absorbed  by  a  body  is  generally  converted 
into  heat.  This  is  not  always  true;  for  example,  much  of  the 
radiant  energy  from  the  sun  which  is  absorbed  by  vegetation 
is  converted  into  chemical  action.  Radiant  energy  is  supposed 
to  be  propagated  in  the  form  of  waves  and  such  a  source  as  the 
sun  emits  this  kind  of  energy  of  many  wave-lengths.  Radiant 
energy  of  a  certain  range  of  wave-lengths  is  capable  of  exciting 
the  sensation  of  light.  The  invisible  rays  of  shorter  wave- 
length than  visible  rays  are  called  ultra-violet  and  the  invisible 
rays  of  longer  wave-length  are  termed  infra-red. 

Just  as  ordinary  objects  are  more  or  less  transparent  to  radia- 
tion of  various  wave-lengths  (spectral  colors)  so  are  different 
objects  more  or  less  transparent  to  the  various  invisible  rays. 
For  example,  water  is  quite  transparent  to  the  visible  rays  and 
is  opaque  to  nearly  all  the  infra-red  rays.  For  this  reason  much 
of  the  infra-red  radiation  emitted  by  the  sun  is  absorbed  by  the 
water  vapor  in  the  atmosphere.  Similarly  the  extremely  short 
ultra-violet  energy  which  is  emitted  by  the  sun  does  not  reach 
the  earth  although  the  spectrum  of  sunlight  shows  that  con- 
siderable quantities  of  ultra-violet  energy  between  0.295/1  and 
the  visible  spectrum  (violet  limit  about  0.39^)  reach  the  earth. 

There  is  much  less  energy  associated  with  a  lumen  of  sunlight 
than  with  the  same  quantity  of  artificial  light  owing  to  the 
absorption  of  much  of  the  infra-red  radiation  by  the  atmosphere 
and  to  other  reasons.  However,  owing  to  the  enormous  inten- 
sities of  daylight  illumination  the  actual  amount  of  energy  which 
reaches  the  earth's  surface  is  great.  If  a  glass  could  be  made 
which  would  not  transmit  any  infra-red  rays  it  should  be  desir- 


214  THE  LIGHTING  ART 

able  in  some  cases  for  use  in  skylights.  An  approximation  to 
this  can  be  obtained. 

The  foregoing  is  well  exemplified  in  a  greenhouse  covered 
with  glass.  Glass  is  opaque  to  some  of  the  infra-red  rays  of 
long  wave-lengths  but  it  transmits  the  infra-red  rays  of  shorter 
wave-lengths.  After  the  radiant  energy  enters  the  green- 
house through  the  glass  some  of  it  is  absorbed  and  changed  into 
heat  energy.  This  results  in  heating  the  object  which  absorbs 
it  and  the  object  now  acts  as  a  radiator  similar  to  the  sun  but  of 
a  very  much  lower  temperature.  Nevertheless  it  emits  radiant 
energy  but  having  a  low  temperature  the  radiation  is  all  of  very 
long  wave-lengths.  This  energy  cannot  escape  through  the 
glass  and  is  therefore  trapped  and  must  expend  itself  largely  as 
heat;  hence  the  interior  of  such  a  glass-covered  house  becomes 
appreciably  hotter  than  the  surroundings.  There  are  many 
other  interesting  details  but  the  foregoing  may  give  an  idea  of 
an  effect  which  is  of  interest  to  lighting  specialists. 

Rooms  of  northern  exposure  are  often  made  more  cheerful 
by  using  hangings  and  shades  having  a  warm  yellowish  tint. 
It  appears  that  this  idea  might  be  carried  further  for  the 
psychological  effect  upon  the  occupants  of  an  interior.  For 
example,  the  north  rooms  in  an  office  building  are  not  cheerful 
and  inviting  for  a  large  part  of  the  year  owing  to  the  coldness 
of  the  light.  It  is  not  generally  practicable  to  overcome  this 
entirely  by  window  hangings  and  decorations.  However,  it  is 
possible  to  make  a  window-glass  of  a  slight  yellowish  tint  (a 
warm  tint,  not  amber)  and  this  could  be  installed  permanently 
in  the  north  windows.  The  author  has  tried  this  on  a  small 
scale  and  the  effect  is  extremely  pleasing.  In  this  manner  the 
north  rooms  of  art  museums  and  other  interiors  could  be  made 
as  inviting  as  the  other  rooms. 

Although  natural  lighting  is  full  of  interest  outdoors  it  does 
not  enjoy  the  highest  favor  in  interiors  because  it  is  difficult  to 
control.  Furthermore,  it  loses  much  of  its  variety  indoors  and 
that  which  it  still  possesses  is  usually  the  undesirable  variety 
in  intensity  which  makes  it  undependable.  It  is  often  stated 
that  one  of  the  great  virtues  of  daylight  is  that  it  is  free,  but 
this  is  not  true  indoors.  The  constructional  cost  of  windows 


NATURAL  LIGHTING  215 

and  roof  skylights  is  usually  greater  than  for  ordinary  walls 
and  roofs  and  sometimes  this  cost  is  much  greater.  Light- 
courts  are  installed  at  the  sacrifice  of  ground  and  floor  areas, 
which  is  a  costly  item  in  cities.  Windows  sometimes  occupy 
valuable  wall  areas  and  there  is  a  maintenance  cost  which  is 
appreciable.  Furthermore,  architects  appreciate  the  exces- 
sive radiation  of  heat  by  glass  and  consequently  allow  an 
additional  capacity  in  the  heating  system  depending  upon  the 
area  of  glass  exposed  to  the  weather.  On  combining  these  cost 
data  with  the  disadvantages  of  daylight  from  the  standpoints 
of  control  and  dependability,  it  is  seen  that  it  is  possible  for 
artificial  light  to  compete  with  natural  light  in  some  interiors 
today  and  perhaps  in  many  interiors  in  the  future. 

The  dominant  direction  of  daylight  in  most  interiors  is  usually 
oblique  and  from  one  or  two  sides.  This  is  quite  different  from 
the  usual  dominant  direction  of  artificial  light.  The  ideal  illu- 
mination in  many  work-rooms  which  are  used  after  dark  would 
be  to  have  the  distribution  of  the  natural  and  artificial  light 
approximately  the  same  provided  this  can  be  done  without 
making  a  sacrifice  in  either  case.  Many  interesting  facts  may 
be  gleaned  from  a  study  of  the  distribution  of  natural  light 
in  interiors,  preferably  by  measurements,  but  much  of  value 
may  be  gained  by  observation.  The  relative  amount  of  dif- 
fused light  is  usually  greater  in  interiors  illuminated  by  natural 
light  than  by  artificial  light;  that  is,  the  shadows  are  usually 
more  luminous.  From  this  standpoint,  indirect  lighting  is 
usually  comparable  with  natural  lighting;  however,  this  system 
of  lighting  more  nearly  simulates  the  distribution  of  light  out- 
doors on  an  overcast  day  than  any  other  distribution  of  day- 
light.1 It  is  an  interesting  experiment  to  simulate  the  distri- 
bution of  daylight  in  an  interior  by  means  of  dummy  windows 
illuminated  by  artificial  light.  The  utilization  efficiency  of 
rooms  illuminated  by  daylight  entering  windows  was  found  in 
three  cases  which  were  investigated  to  be  from  17  to  33  per  cent. 
That  is,  these  are  the  percentages  of  the  total  lumens  entering 
the  windows  which  were  effective  on  the  ordinary  horizontal 

1 M.  LUCKIESH:  "  Natural    and    Artificial  Light-distribution   in  Interiors," 
Trans.  I.  E.  S.,  7,  388,  1912. 
15 


216  THE  LIGHTING  ART 

work-plane.  Observations  along  this  line  yield  much  interest- 
ing data  and  at  least  stimulate  thoughts  which  lead  the  lighting 
specialist  out  of  the  ruts  of  common  procedure.  Many  in- 
teresting details  could  be  discussed  but  the  aim  has  been  to 
awaken  an  interest  among  lighting  specialists  with  the  hope  that 
they  will  make  such  observations  and  analyses  in  order  to 
become  more  intimately  acquainted  with  lighting. 

Although  it  is  difficult  to  control  daylight  and  this  may  seldom 
be  done  with  the  satisfactoriness  with  which  artificial  light  is 
controlled,  there  are  various  means  which  are  helpful  aids. 
There  is  available  an  extensive  variety  of  glasses  such  as  sand- 
blasted, etched,  opal,  ribbed,  pebbled,  and  "refractive"  from 
which  the  most  suitable  may  be  selected.  However,  a  proper 
selection  will  depend  upon  a  knowledge  of  simple  optical  laws 
and  upon  the  many  details  of  a  specific  condition.  There  are 
many  designs  of  prism  glass  available  and  the  proper  selection 
and  installation  for  a  specific  case  must  depend  upon  judg- 
ment backed  by  a  knowledge  of  the  simple  optical  laws.  Shades 
shutters,  and  louvers  are  also  valuable  accessories  in  natural 
lighting.  Even  the  painting  of  surfaces  of  light-courts,  walls  of 
adjacent  buildings,  and  the  surroundings  in  interiors  is  an 
important  aspect  in  natural  lighting.  In  fact,  owing  to  the 
usual  handicap  of  the  location  of  windows  in  the  walls,  the  best 
results  in  distributing  daylight  in  interiors  will  be  obtained  only 
through  exercising  much  ingenuity.  Some  of  the  redeeming 
features  of  natural  lighting  are  the  usual  excessive  quantity 
available,  the  adaptation  of  the  eyes  to  a  high  level  of  illumina- 
tion, the  low  brightness  of  the  source  which  is  generally  the 
sky,  and  the  amount  of  diffused  light. 


CHAPTER  XXIV 
THE  LANGUAGE  OF  COLOR 

In  mythology  the  fact  is  revealed  that  color  has  impressed 
mankind  long  before  the  beginning  of  written  history  and  from 
a  study  of  the  primitive  races  of  today  it  appears  safe  to  con- 
clude that  the  influence  of  color  upon  the  human  organism  began 
in  an  early  stage  of  the  evolution  of  man.  There  is  a  degree  of 
consistency  in  certain  psycho-physiological  effects  of  a  few 
fundamental  colors  which  warrants  the  formulation  of  the 
title  of  this  chapter.  Owing  to  these  effects  it  may  be  said  that, 
at  the  present  time,  colors  possess  certain  innate  powers  or 
attributes  which  affect  the  human  organism  without  the  neces- 
sity for  an  accompanying  associational  mental  process.  How 
this  influence  has  developed  is  of  scientific  interest  but  it  need 
not  be  discussed  here.  However,  it  can  be  shown  how  certain 
agencies  such  as  Nature,  the  consistent  and  persistent  usage 
of  colors  in  ecclesiasticism,  in  painting,  in  the  theatre,  and  in 
many  activities  in  daily  life,  the  interpretations  of  poets  and 
mental  associations  have  welded  certain  attributes  to  various 
colors  with  the  result  that  we  have  a  meager  though  definite 
language  of  color. 

But  it  should  be  emphasized  that  our  definite  knowledge  of 
the  expressiveness  and  impressiveness  of  color  is  extremely 
limited  and  that  the  effusions  on  this  subject  by  those  who 
possess  at  best  only  a  superficial  acquaintence  with  the  intricate 
fabric  of  color-science  are  mixtures  of  fact  and  fancy  with  a 
superabundance  of  the  latter.  However,  the  earnest  student 
of  this  subject  finds  sufficient  definite  and  consistent  data  in 
various  indirectly  associated  fields  to* encourage  further  ex- 
ploration, study  and  experiment  which  may  aid  in  a  more 
scientific  use  of  color.  Color  is  a  medium  capable  of  creating 
pleasure  and  this  should  be  a  sufficient  stimulus  to  the  lighting 
specialist  to  inspire  him  to  attempt  to  utilize  its  power  in 
lighting.  To  those  who  have  opened  their  eyes  to  the  fact 

217 


218  THE  LIGHTING  ART 

that  lighting  should  be  considered  more  from  the  psychological 
than  from  the  engineering  standpoint  in  nearly  all  aspects  of 
the  field,  no  plea  for  utilizing  color  in  light  is  necessary. 

A  great  difficulty  is  encountered  in  the  use  of  color  in  lighting, 
which  is  equally  true  of  many  other  activities ;  namely,  in  recog- 
nizing the  boundary  between  fact  and  fancy  or  between  the 
psycho-physiological  effects  upon  mankind  as  a  whole  and  that 
which  we  call  taste.  Taste  is  individualistic  and  largely  a 
personal  right;  therefore  it  may  be  said  to  be  indeterminate. 
Although  individual  taste  should  be  respected,  it  is  not  neces- 
sary to  such  an  extent  that  some  of  the  generalities  of  esthetics 
are  permitted  to  be  violated.  However,  there  are  certain  fun- 
damental effects  of  various  colors  upon  the  human  organism 
regardless  of  personality  and  these  the  lighting  specialist  may 
utilize  as  a  foundation  for  any  attempt  at  utilizing  color  in 
lighting  for  its  psycho-physiological  influence  or  for  its  decorative 
and  artistic  effect.  Only  this  meager  basis  may  be  used  gener- 
ally for  when  the  personality  of  a  client  enters  it  should  be 
remembered  that  the  effects  of  colors  will  depend  upon  the 
individual  owing  to  the  influences  of  intellectual  development, 
experiences  and  temperament  of  the  individual. 

Owing  to  the  indefiniteness  of  the  language  of  color  it  is 
impossible  to  discuss  it  completely  in  a  brief  chapter  because 
of  the  necessity  for  so  much  qualifying  material;  however,  it 
appears  of  value  to  touch  upon  the  subject  for  whatever  the 
material  which  is  presented  may  be  worth  and  as  a  sort  of 
prophetic  valedictory.  At  least  it  may  be  of  value  in  inciting 
thought  and  observation  along  a  line  which  will  be  profitable 
to  the  lighting  specialist  who  may  be  thus  encouraged  or 
inspired.  The  subject  may  be  readily  studied  by  making  obser- 
vations on  every  hand  and  by  delving  into  such  fields  as 
mythology,  ecclesiasticism,  poetry,  painting,  decoration,  architec- 
ture, Nature,  the  theatre,  and  various  symbolic  uses  of  color  in 
daily  practice.  A  volume  has  been  prepared1  which  aims  to 
present  the  data  gleaned  from  these  and  other  sources.  Por- 
tions of  Chapter  IX  may  be  considered  as  prefatory  to  the 
present  discussion. 

*M.  LUCKIESH:  The  Language  of  Color  (in  press). 


THE  LANGUAGE  OF  COLOR  219 

In  order  not  to  be  led  too  far  afield  only  a  few  of  the  most  con- 
spicuous colors  will  be  treated.  Space  will  not  permit  going 
far  into  detail  but  it  should  be  noted  that  such  factors  as  asso- 
ciations and  usage  are  important  influences  in  molding  the 
meager  language  of  color  which  is  available  today.  Further- 
more, a  color  may  possess  many  attributes  depending  upon  its 
environment,  its  saturation  or  purity,  the  association  which  it 
arouses  owing  to  its  particular  use,  the  occasion,  etc.  From  a 
consideration  of  these  factors  and  encouraged  by  the  definite- 
ness  of  the  data  given,  it  is  hoped  the  lighting  specialist  will 
find  it  easy  to  extend  his  horizon  regarding  this  interesting  and 
potential,  though  uncultivated,  aspect  of  lighting.  Aside 
from  this  broader  view  of  the  use  of  color  in  lighting  there  are 
purely  utilitarian  uses  which  may  be  directed  more  or  less  by 
the  facts  of  the  symbolic  usage  of  color.  All  of  these  cannot  be 
presented  but  the  few  that  are  given  should  inspire  a  more  con- 
sistent and  general  utilitarian  usage  of  colored  light.  In  many 
applications  of  colored  light  the  decorative  scheme  must  be 
controlled  and  even  called  upon  to  aid  in  carrying  out  the  de- 
sired effect. 

Red  is  universally  considered  to  be  stimulating  or  exciting 
and  this  has  been  proved  by  experiment.  The  nerves  are  in  an 
excited  state  and  it  has  been  shown  that  the  amount  of  certain 
kinds  of  work  which  can  be  done  in  a  given  period  of  time  is 
augmented  under  red  light;  Its  effect  is  similar  to  that  of 
other  stimulants  in  this  respect  and  its  continued  use  would  be 
as  readily  condemned.  In  the  lighter  tints  it  becomes  mildly 
stimulating  and  rose,  which  is  a  tint  of  a  reddish-purple,  is 
delightfully  stimulating  in  a  mild  manner.  For  this  reason 
light  of  a  barely  perceptible  rose  tint — more  felt  than  seen— 
is  appropriate  for  living  and  dining  rooms  on  certain  occasions 
and  in  ballrooms,  restaurants,  etc.  Light  tints  of  red  and  even 
red  combined  with  white  have  been  used  symbolically  to  sug- 
gest blooming  youth,  health,  and  happiness. 

Perhaps  the  most  general  association  which  is  coupled  with 
red  is  blood.  For  this  reason  it  has  been  endowed  with  ap- 
propriate attributes  in  poetry,  mythology,  etc.  It  has  been 
the  flag  of  war  and  has  ornamented  the  shield  of  tried  manhood, 
being  the  badge  of  valor,  superiority  and  prowess. 


220  THE  LIGHTING  ART 

Perhaps  its  most  general  utilitarian  use  is  as  a  signal  of  dan- 
ger and  this  is  an  excellent  example  of  the  influence  of  persistent 
usage  for  in  its  proper  environment  red  is  always  recognized  as 
indicating  danger.  It  is  perhaps  the  most  striking  color  and 
apparently  is  the  first  to  be  named  by  the  savage  as  he  begins 
to  ascend  the  ladder  of  intelligence. 

It  shares  with  blue  the  highest  rank  in  the  scale  of  preference 
when  this  is  based  upon  color  uninfluenced  by  associations  as 
completely  as  possible.  There  is  strong  evidence  that  it  is 
more  preferred  by  females  than  any  other  color.  These  con- 
clusions are  based  upon  scientific  experiments  in  which  the  proper 
control  of  various  factors  has  been  exercised  as  far  as  possible. 

Yellow  in  its  warmer  hues  and  orange  possess  the  same  stimu- 
lating characteristic  as  red  though  of  a  milder  degree.  It  is 
interesting  in  this  respect  to  note  that  shades  and  tints  of  yel- 
low are  used  predominantly  in  decorating  interiors.  Perhaps 
this  has  arisen  from  the  psychological  effect  of  this  color  which 
imparts  warmth  to  an  interior  and  logically  it  is  one  of  the  aims 
in  housing  to  provide  a  cheerful,  inviting,  and  protective  en- 
vironment. Of  further  interest  in  lighting  is  the  warm  yellow- 
ish tint  of  nearly  all  the  early  illuminants  which  through  the 
persistence  of  habit  have  added  their  influence  in  creating  the 
desire  for  illuminants  of  a  warm  color  in  interiors.  These  may 
be  obtained  by  means  of  tinted  lamps,  screens  and  glassware 
and  the  same  effect  may  be  obtained  by  indirect  systems  of 
lighting  in  rooms  whose  walls  and  ceiling  are  yellowish  in  hue. 
The  finer  color-sensibility  manifests  itself  in  an  aversion  toward 
amber — a  greenish-yellow — which  is  sometimes  considered 
by  the  uninitiated  to  be  a  substitute  for  warm  yellow. 

Yellow  is  a  luminous  color  and  is  often  associated  with  sun- 
light although  strictly  the  latter  is  not  yellow  except  during 
sunrise  and  sunset.  However,  it  appears  yellowish  by  contrast 
with  blue  skylight.  Being  warm,  luminous,  and  associated 
with  the  sun,  yellow  has  been  symbolic  of  fire. 

The  attribute  of  abundance  has  been  bestowed  upon  yellow 
doubtless  through  association  in  Nature  with  the  bountiful 
harvest  because  this  is  a  common  color  of  ripened  crops. 

This  color  has  been  widely  used  by  poets  to  symbolize  jeal- 


THE  LANGUAGE  OF  COLOR  221 

ousy  but  usually  a  greenish-yellow  is  described  or  implied. 
It  has  also  been  used  to  symbolize  inconstancy  and  deceit 
though  in  this  office  an  impure  or  soiled  yellow  is  usually  im- 
plied. For  example,  the  garb  of  Judas  is  often  described  as 
being  of  a  dirty  yellow  and  the  custom  has  been  in  vogue  in  past 
centuries  of  using  yellow  on  the  doors  of  the  abodes  of  felons. 

It  has  been  quite  generally  used  to  symbolize  sickness;  hence 
it  is  the  flag  of  quarantine  and  has  been  used  to  indicate  field 
hospitals  in  war. 

Green  is  most  characteristically  described  as  being  a  neutral 
color.  Perhaps  its  abundance  in  Nature  has  gradually  subdued 
any  striking  influence  it  might  have  had  on  the  human  organism 
and  doubtless  continued  adaptation  to  this  color  in  natural 
environments  has  rendered  it  neutral.  There  is  no  doubt  about 
this  characteristic  and  hence  shades  and  tints  of  green  are 
proper  colors  for  certain  interiors.  The  applications  of  green 
light,  however,  appear  to  be  extremely  limited  although  scien- 
tific investigation  may  indicate  certain  desirable  psycho- 
physiological  effects  which  may  be  utilized  in  the  future.  It  has 
a  place  in  lighting  as  a  vital  or  contrasting  spark  in  certain  at- 
tempts which  may  be  made  to  "paint"  with  light.  It  is  used 
to  symbolize  perpetuity  as  "evergreen  memory'7  and  the  prac- 
tice of  placing  green  foliage  upon  the  graves  of  the  dead  is  one 
of  fine  sentiment.  Doubtless,  due  to  the  fact  that  green  is  the 
conspicuous  color  of  springtime,  this  color  is  used  to  symbolize 
youth,  immature  judgment,  vigor,  freshness,  and  hope. 

Blue  is  a  cold  color,  the  degree  depending  upon  its  exact  hue 
and  purity.  When  it  inclines  toward  violet  it  appears  to  lose 
this  attribute  and  to  become  restful.  Blue  is  of  low  luminosity 
and  being  cold  is  somewhat  depressing  when  used  in  lighting. 
However,  it  may  be  used  to  advantage  sometimes  when  it  in- 
clines in  hue  toward  green.  For  example,  a  theatre  in  mid- 
summer seems  to  be  much  more  comfortable  when  illuminated 
by  blue  or  blue-green  light.  It  is  thus  seen  that  an  attribute 
of  a  color  which  ordinarily  may  be  unpopular,  can  be  used  to 
advantage  in  a  proper  place.  Many  such  applications  of  colored 
light  fall  within  the  province  of  the  lighting  specialist. 

Certain  tints  and  hues  of  blue  appear  to  possess  the  attribute 


222  THE  LIGHTING  ART 

of  serenity,  at  least  this  has  been  bestowed  upon  them.  This 
may  arise  through  the  restfulness  of  these  colors  but  it  is  inter- 
esting to  note  that  the  finer  sensibilities  have  recognized  the 
serenity  of  the  blue  sky  and  of  Nature's  solitudes.  In  the 
latter  case  the  illumination  often  is  chiefly  due  the  blue  sky- 
light. Owing  to  the  dominating  presence  of  blue  sky  in  natural 
scenes  this  color  has  also  been  looked  upon  as  possessing  a 
harmonizing  influence  because  in  Nature  it  is  a  color  which 
is  nearly  always  present  in  any  scene. 

Perhaps  owing  to  the  fact  that  it  is  the  color  of  the  heavens — 
the  abode  of  the  Gods — mythology  has  also  bestowed  upon 
this  color  the  attribute  of  intelligence.  Many  interesting 
speculations  arise  in  the  study  of  the  language  and  symbolism 
of  color.  For  example,  blue  eyes  are  very  common  and  the 
eyes  are  closely  associated  with  the  intellect  and  personality. 
From  these  reasons  the  attribute  of  intelligence  may  have  partly 
arisen  or  Minerva  may  have  been  considered  the  " blue-eyed" 
progeny  of  Jove  for  similar  reasons. 

As  blue  inclines  toward  violet  or  toward  a  deep  shade  (corre- 
sponding to  a  lower  intensity  when  applied  to  light)  it  has  been 
characterized  as  restful,  quiet,  dejected  and  even  dismal.  It 
is  easy  to  account  for  these  attributes  partially  through  our 
experiences  with  Nature. 

Purple  has  scanty  application  in  lighting  though  it  appears 
to  be  characterized  by  certain  attributes  and  symbolic  uses. 
It  has  been  chiefly  characterized  as  dignified,  stately,  sedate, 
solemn,  and  pompous  and  has  long  been  the  garb  of  royalty. 
The  latter  is  another  example  of  the  influence  of  usage  for 
doubtless  it  became  the  color  of  royal  robes  because  in  the  early 
centuries  of  civilization  it  was  a  rare  and  costly  color.  For 
this  reason  it  became  the  mark  of  royalty  and  wealth.  It  is 
sometimes  used  in  mythology  and  poetry  as  the  color  of  blood 
which  is  a  more  correct  usage  than  red  for  the  same  purpose; 
therefore,  it  was  used  symbolically  in  appropriate  ways.  Rose, 
a  tint  of.  purple,  has  already  been  discussed. 

White  naturally  assumed  the  attributes  of  chastity,  vir- 
ginity, purity,  innocence,  fidelity,  peace  and  friendship;  and 
mythology  and  poetry  abound  with  examples  of  such  usage. 


THE  LANGUAGE  OF  COLOR  223 

It  also  symbolizes  weakness  perhaps  through  association  with 
femininity  and  was  the  mark  of  untried  manhood.  Consistently 
therefore  it  is  appropriately  the  flag  of  surrender  and  of  truce. 

Black  naturally  is  quite  opposite  in  character  to  white,  being 
characterized  as  dismal,  desolate,  deadly,  malignant,  threaten- 
ing, evil,  chaotic  and  loathesome.  Its  symbolic  uses  are  very 
numerous  and  consistent  as  is  true  of  white.  It  is  evident  why 
it  is  almost  universally  used  in  mourning  and  in  various  other 
ways.  It  has  its  place  in  lighting-effects  for  low  intensity  of 
illumination  or  the  absence  of  light  in  the  proper  places  in  an 
interior  is  a  potent  factor  in  lighting-effects. 

Many  other  colors  and  combinations  of  colors  appear  to  have 
symbolic  uses  or  attributes  seemingly  appropriate.  For  ex- 
ample, gray  which  lies  between  white  and  black  partakes  of 
the  attributes  of  both  and  by  this  mixture  or  balance  assumes 
a  r61e  lying  conspicuously  between  them.  Attributes  are 
bestowed  upon  it  which  are  quite  the  same  as  those  bestowed 
upon  black  and  white  when  used  together.  In  fact,  the  whole 
labric  of  the  language  of  color  as  obtained  from  many  different 
sources  appears  to  be  solidly  interwoven,  but  there  are  so  many 
aspects  that  it  is  easy  to  go  astray  in  examining  it. 

Much  of  the  information  gained  from  a  study  of  this  character 
may  be  applied  only  indirectly;  however,  it  is  valuable  to  the 
lighting  specialist  for  it  deals  with  color  and  therefore  with 
light.  Lights  of  all  colors  have  at  least  decorative  value  and 
must  be  applied  in  this  respect  according  to  the  principles  of 
harmony. 

There  are  no  laws  of  harmony  which  can  be  stated  in  a  few 
words  because  such  a  statement  resolves  into  a  description 
of  a  single  harmony.  However,  it  may  be  noted  that  in  deal- 
ing with  colors  there  is  the  principle  harmony  of  sequence  and 
that  of  contrast.  According  to  the  former  the  hues  of  the  colors 
used  are  closely  associated  in  the  spectrum  or  a  sequence  of 
approximately  the  same  hue  is  arranged  in  respect  to  tint  or 
shade.  According  to  the  principle  of  harmony  of  contrast 
the  colors  are  contrasting,  or  far  apart  in  hue. 

It  is  confidently  predicted  that  the  aspect  of  color  considered 
in  this  closing  chapter  will  be  an  important  one  in  lighting 


224  THE  LIGHTING  ART 

at  some  future  time  for  it  represents  the  climax  of  the  expres- 
siveness of  light.  Therefore  it  is  the  logical  climax  of  an 
attempt  to  present  a  broad  view  of  lighting  in  so  far  as  the  space 
of  a  brief  volume  permits.  It  is  hoped  that  some  of  the 
material  presented  in  these  chapters  will  be  of  immediate  value; 
that  some  of  it  will  suggest  new  ideas;  and  that  the  whole  has 
revealed,  to  a  small  degree  at  least,  the  potentiality  of  light 
and  lighting. 


INDEX 


Accidents,  172 
Acetylene  flame,  62 
Additive  colors,  68 
Advertising,  color  in,  75 
After-image,  73 
Alcove,  145 
Altar,  169 

Aluminized  surface,  111 
Appearance  of  an  object,  119 
Architect,  114,  132 
Architectural  details,  115 
Architecture,  6,  12,  20,  113,  189, 
Art  appreciation,  116 

galleries,  88 

studio,  90 
Artist,  lighting,  40 
Association,  217 
Asymmetry,  22,  31 
Atmospheric  absorption,  96 
Auditorium,  160,  167 

Background,  154,  177 
Bathroom,  143 
Beauty  and  utility,  6,  39 
Bed  chamber,  142 
Black,  223 
Blue,  221 

light,  97 

prints,  17 
Border  lights,  151 
Brackets,  136,  138,  143 
Brightness,  33,  118 

contrast,  117,  134 

units,  207 

vs.  illumination,  16,  28,  35 

Candle,  201 

flame,  61 
Candlepower,  202 
Carbon  arc,  62 

dioxide  tube,  62,  82,  86 
Central  station,  132 


Chancel,  168 
Chandeliers,  44,  140,  165 
Checkerboard  color-screens,  70 
Chemical  analysis,  91 
Churches,  168 
Cigar  factory,  88 
Class  room: 

width  of,  159 

window  area  of,  159 
Clear  glass,  104 
Coefficient  of  utilization,  204 
217      Cold  colors,  76 
Color,  48,  215 

and  ilium  inants,  57 

and  light,  48 

and  variety,  23 

distortion  of,  55 

factory,  89 

impressiveness  of,  1,  Chap.  24 

in  lighting,  6,  77 

language  of,  215 

light,  shade  and,  18 

mixture,  66 

of  illuminants,  56 

preference,  75 

printing,  90 

science,  8 

screens,  184 

subjective,  57 

vision,  71 

wheel,  184 
Colored  glass,  62,  77 

light,  94,  169 

media,  53,  55,  62 
and  illuminants,  57 
impurity  of,  54 
spectra  of,  54 
Colors,  attributes  of,  76 

complementary,  58 

number  of,  59 

primary,  67 

symbolism,  219 
225 


226 


INDEX 


Commercial  lighting,  147 
Computations,  197 
Concealed  lighting,  190 
Cones,  72 
Contractor,  132 
Contrast,  10 

simultaneous,  72 

successive,  73 

Control  of  lighting,  135,  175 
Cooperation  in  lighting,  132 
Cosine  law,  201 
Cotton  exchange,  89 
Cove-lighting,  34,  118 
Creation  vs.  imitation,  9 

Daylight,  22,  34,  60,  119,  150,  209 

and  artificial  light,  36 

artificial,  14,  78,  81,  85,  165 

cost  of,  3,  212 

distribution  of,  210 

intensity  of,  199,  211 

modifying,  100 

openings,  209 

simulating,  80 

variation  of,  80,  209 
Decoration,  12,  19,  79,  117,  218 
Decorative  pattern,  113,  119 
Decorator,  132 
Danger  signal,  97 
Dark-room,  photographic,  95 
Den,  143 
Dentistry,  92 
Depreciation,  175 
Diffused  light,  30 
Dining  room,  138 

unit,  140 

Direct-  indirect  units,  32 
Direction  of  light,  160 
Display  cases,  166 
Distribution  of  light,  11,  19,  22,  24, 
27,  116,  136 

from  fixtures,  46      • 
Dome,  139 
Dyes,  65 

Ecclesiasticism,  77,  218 
Edridge-Green,  72 
Efficiency,  illuminating,  148 
Elliptical  mirror,  108 


Emergency  lighting,  167 
Enamelled  surface,  111 
Engineer,  illuminating,  5 
Esthetics,  79,  134 
Exposure,  77 
Expressiveness  of  light,  10 

of  pigments,  11 
Eye,  199 

fatigue,  93 

Fading,  166 
Filters,  colored,  55 
Fixture,  central,  136 

dealer,  132 
Fixtures,  21,  38,  117,  120 

buying,  41 

designing,  38 

faulty,  43 

obsolete,  45 

role  of,  42 

selling,  40,  122 
Flaming  arc,  62,  82,  86 
Flood-lighting,  190 
Flour  mill,  92 
Fluorescence,  53 
Focal  length,  109 
Focus,  108 
Foot-candle,  201 

lights,  151,  182 
Fountain,  121,  193 
Fur,  90 

Garment  factory,  89 
Gas  flame,  62 

mantle,  62,  82 
Gelatines,  colored,  64,  66 
Germicidal  action,  98 
Glare,  96,  134,  174 
Glass,  caps,  63 

clear,  104 

prism,  109 

skylight,  120 
Glassware,  colored,  63 
Glossy  surfaces,  161 
Green,  221 

Hallway,  145 
Harmony,  79,  223 
Helium  tube,  62 


f 

Hering  theory,  71 
Home  lighting,  132 
Hue,  58 
Hues,  complementary,  58 

Uluminants,  artificial,  56 

colored,  55,  60 

color  of,  11,  13,  60 
Illumination,  art  of,  40 

intensities,  199,  204 

vs.  brightness,  16,  28,  134 
Elusions,  12,  116 
Imagination,  16 
Imitation  vs.  creation,  9 
Impregnating  salts,  62 
Incandescent  lamps,  61 
Industrial  lighting,  171 
Infra-red  rays,  100 

absorption  of,  212 
Intensity  of  illumination,  171, 

204 

Inverse-square  law,  201 
Invisible  radiation,  212 
Irradiation,  117 

Jewels,  149,  92 
Jones,  Bassett,  55 
Judgment  of  color,  150 
Juxtapositional  mixture,  69 

Kitchen,  144 

Lacquers,  colored,  64 
Ladd-Franklin,  72 
Lamps,  bare,  134 

for  stage,  184 
Language  of  color,  217 
Lattice,  145 
Laundry,  92 
Law,  cosine,  201 

inverse-square,  201 

visual,  199 
Layout,  198 
Lens,  108 
Light: 

and  color,  48 

colored,  52 

control,  101 

court,  160 


INDEX 


227 


Light,  definition  of,  48 

direction  of,  160 

expressiveness    of,     10,    Chap. 
24 

impressiveness    of,    10,    Chap. 
24 

painting  with,  11,  26 

production  of,  2 

shade  and  color,  18 

sources,  4,  44 

tinted,  13,  25 

white,  49,  55 
Lighting  and  progress,  2 

and  sociology,  2 

and  the  arts,  1 

and  vision,  176 

artist,  161 

artistic,  5 

broad  aspect  of,  1,  17 
200,  commercial,  147 

control,  135,  175 

distribution  of,  11 

effects,  6,  18 

emergency,  167 

harmful,  4 

hygiene  of,  133 

industrial,  171 

outline,  189 

potentiality  of,  1,  4 

problem  of,  197 

protective,  172 

psychology  of,  217 

public  buildings,  158 

residence,  132 

spectacular,  189 

stage,  180 

systems,  31 

units,  21,  24,  31,  38 

variety  in,  21 
Living  room,  135 
Localized  lighting,  175 
Louvers,  165 
Lumen,  203 
Luminous  flux,  203 

Maintenance,  176 
Mazda  C-2  lamp,  84 

C-3  lamp,  94 
Medicine,  93 


228 


INDEX 


Mercury  arc,  51,  61,  74,  82,  97 
Metal  work,  91 
Microscopy,  88 
Mirror,  parabolic,  106 

spherical,  105 
Mirrored  reflectors,  111 
Mixing  colored  lights,  186 
Mixture  of  lights,  195 

of  natural  and    artificial  light, 

151,  173 

Mobile  color,  182,  187,  194 
Monotony,  22 
Moonlight,  65 
Moore  tube,  62,  86 
Mounting  height,  198 
Moving-picture  theatre,  169 

screen,  170 
Mural  painting,  121 
Museums,  88,  161 
Mythology,  77,  215 

Natural  lighting,  210 
Nature,  10,  14,  21,  23,  26,  77,  212 
Neon  tube,  62 
Neutral  colors,  76 
Nitrogen  tube,  62 
North  exposure,  162,  211 
glass  for,  77 

Old  illuminants,  simulating,  99 

Opal  glass,  111 

Ore  refinery,  91 

Outlets,  21,  131,  137,  173 

provision  for,  121 

spacing  of,  198 
Outline  lighting,  189 
Overshooting  of  sensations,  73 

Paint  shops,  89 
Painting,  77,  216 

with  light,  79,  131 
Paintings,  79 

galleries,  162 

Panama-Pacific  Expo.,  193 
Panel,  115 
Paper  mill,  92 
Penumbra,  29 
Phosphorescence,  53 
Photographic  emulsions,  95 


Photography,  94 
Physiology  of  color,  71 
Pigments,  10,  65 
Poetry,  77,  218 
Portable  lamps,  137 
lighting  unit,  122 

direct-indirect,  129 

new,  128 

unique,  131 

Primitive  language,  77,  216 
Prism  glass,  109,  154 
Prismatic  glassware,  111 
Projection  apparatus,  185 

screen,  170 

Protecting  the  eyes,  177 
Protective  lighting,  172 
Psycho-physiology,  71 
Public  buildings,  158 
Purkinje  effect,  73 
Purple,  56,  57,  222 

Quality  of  light,  27 

Rainbow,  49 

Range  of  signals,  96 

Rare  earth,  62 

Reading,  134 

Red,  217 

Reflection  characteristics,  102 

total,  110 
Reflectors,  colored,  65 

and  spacing,  198 
Relief,  117 

Residence  lighting,  132 
Retinal  sensitivity,  74 
Rod  and  cone  theory,  72 
Rods,  72 
Rug  rack,  152 
Ryan,  W.  D'A.  55,  192 : 

Safety,  8 
Saturation,  58 
Schools,  158 
School-rooms,  160 
Scintillator,  192 
Sculpture  gallery,  165 
Semi-indirect  units,  33 
Sensations,  achromatic,  17 
chromatic,  17 


INDEX 


229 


Shades,  56,  59 
Show-case,  152 

-window,  78,  88,  120,  152,  156, 

206 

Shadows,  28,  118 
Shadow-edge,  118 
Shower,  139 
Signal  lenses,  63 
Signalling,  96 
Silk  shade,  130 
Sky  brightness,  160 
Skylight,  61,  81,  211 
area,  207 
glass,  100,  216 
Smoke,  192,  210 
Solutions,  colored,  66 
South  exposure,  162 
Spacing  of  outlets,  198 
Spectacular  lighting,  189 
Spectra  of  illuminants,  50 
continuous,  51 
line,  51 
Spectral  analysis,  50 

character,  50 
Spectroscope,  66 
Spectrum,  49 
of  gases,  51 
of  solids,  51 
visible,  54 
Stage-effects,  187 
Stage  lighting,  180 
Steam,  192 
Steradian,  202 
Store,  87,  147 

Stores,  artificial  daylight  in,  151 
Study,  143 
Subjective  color,  57 
Subtractive  color,  67 
Sugar  refinery,  92 
Sunlight,  60,  81,  210 

cost  of,  210 
Surgery,  92 

Symbolism  of  color,  219 
Symmetry,  22 


Taste,  218 

Temperature  and  color,  50 

Templates,  69 

Textile  mill,  89 

Textiles,  colored,  64 

Theatres,  169 

Tints,  56,  59 

Transmission  characteristics,  103 

Ultra  violet,  53 

Umbra,  29 

Uniformity  in  lighting  ,121,  198 

Unique  effects,  145 

Utility  and  beauty,  6,  39 

Utilization  coefficient,  204 

Vacuum  tube,  51,  62 
Variety  in  lighting,  21,  137 
Velum,  164 

Visibility  of  radiation,  50 
Vision,  7 

and  lighting,  176 
Visual  acuity,  74,  97 

function,  172 

law,  199 
Visualization,  16 
Von  Kries  theory,  72 

Warm  colors,  76 
White,  220 

light,  49,  55,  60,  81,  84 
Window,  168 

artificial,  25,  145 

clerestory,  165 

flood-lighting,  169 

lighting  value  of,  159 
Wiring,  121 
Woodwork,  92 
Work-plane,  148 

Yellow,  55,  218 

glass,  139 

light,  99 

and  acuity,  98 
Young-Helmholtz  theory,  71 


RETURN  TO  the  circulation  desk  of  any 
University  of  California  Library 
or  to  the 

NORTHERN  REGIONAL  LIBRARY  FACILITY 
Bldg.  400,  Richmond  Field  Station 
University  of  California 
Richmond,  CA  94804-4698 

ALL  BOOKS  MAY  BE  RECALLED  AFTER  7  DAYS 
2-month  loans  may  be  renewed  by  calling 

(510)  642-6753 
1-year  loans  may  be  recharged  by  bringing  books 

to  NRLF 
Renewals  and  recharges  may  be  made  4  days 

prior  to  due  date 

DUE  AS  STAMPED  BELOW 

JUN  2  0  1994 


JUL211997, 


3844 


i ,  r 

UNIVERSITY  OF  CALIFORNIA  LIBRARY 


, 


